arch/microblaze: support get_user() of size 8 bytes

arch/microblaze/ is missing support for get_user() of size 8 bytes,
so add it by using __copy_from_user().

While there, also drop a lot of the code duplication.

Fixes these build errors:
   drivers/infiniband/core/uverbs_main.o: In function `ib_uverbs_write':
   drivers/infiniband/core/.tmp_gl_uverbs_main.o:(.text+0x13a4): undefined reference to `__user_bad'
   drivers/android/binder.o: In function `binder_thread_write':
   drivers/android/.tmp_gl_binder.o:(.text+0xda6c): undefined reference to `__user_bad'
   drivers/android/.tmp_gl_binder.o:(.text+0xda98): undefined reference to `__user_bad'
   drivers/android/.tmp_gl_binder.o:(.text+0xdf10): undefined reference to `__user_bad'
   drivers/android/.tmp_gl_binder.o:(.text+0xe498): undefined reference to `__user_bad'
   drivers/android/binder.o:drivers/android/.tmp_gl_binder.o:(.text+0xea78): more undefined references to `__user_bad' follow

'make allmodconfig' now builds successfully for arch/microblaze/.

Fixes: 538722ca3b ("microblaze: fix get_user/put_user side-effects")
Reported-by: kbuild test robot <lkp@intel.com>
Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Acked-by: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Steven J. Magnani <steve@digidescorp.com>
Cc: Michal Simek <monstr@monstr.eu>
Cc: Jason Gunthorpe <jgg@mellanox.com>
Cc: Leon Romanovsky <leonro@mellanox.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Doug Ledford <dledford@redhat.com>
Signed-off-by: Michal Simek <michal.simek@xilinx.com>

arch/microblaze/include/asm/uaccess.h

@@ -163,44 +163,15 @@ extern long __user_bad(void);
  * Returns zero on success, or -EFAULT on error.
  * On error, the variable @x is set to zero.
  */
-#define get_user(x, ptr)						\
-	__get_user_check((x), (ptr), sizeof(*(ptr)))
-
-#define __get_user_check(x, ptr, size)					\
-({									\
-	unsigned long __gu_val = 0;					\
-	const typeof(*(ptr)) __user *__gu_addr = (ptr);			\
-	int __gu_err = 0;						\
-									\
-	if (access_ok(__gu_addr, size)) {			\
-		switch (size) {						\
-		case 1:							\
-			__get_user_asm("lbu", __gu_addr, __gu_val,	\
-				       __gu_err);			\
-			break;						\
-		case 2:							\
-			__get_user_asm("lhu", __gu_addr, __gu_val,	\
-				       __gu_err);			\
-			break;						\
-		case 4:							\
-			__get_user_asm("lw", __gu_addr, __gu_val,	\
-				       __gu_err);			\
-			break;						\
-		default:						\
-			__gu_err = __user_bad();			\
-			break;						\
-		}							\
-	} else {							\
-		__gu_err = -EFAULT;					\
-	}								\
-	x = (__force typeof(*(ptr)))__gu_val;				\
-	__gu_err;							\
+#define get_user(x, ptr) ({				\
+	const typeof(*(ptr)) __user *__gu_ptr = (ptr);	\
+	access_ok(__gu_ptr, sizeof(*__gu_ptr)) ?	\
+		__get_user(x, __gu_ptr) : -EFAULT;	\
 })
 
 #define __get_user(x, ptr)						\
 ({									\
 	unsigned long __gu_val = 0;					\
-	/*unsigned long __gu_ptr = (unsigned long)(ptr);*/		\
 	long __gu_err;							\
 	switch (sizeof(*(ptr))) {					\
 	case 1:								\
@@ -212,6 +183,11 @@ extern long __user_bad(void);
 	case 4:								\
 		__get_user_asm("lw", (ptr), __gu_val, __gu_err);	\
 		break;							\
+	case 8:								\
+		__gu_err = __copy_from_user(&__gu_val, ptr, 8);		\
+		if (__gu_err)						\
+			__gu_err = -EFAULT;				\
+		break;							\
 	default:							\
 		/* __gu_val = 0; __gu_err = -EINVAL;*/ __gu_err = __user_bad();\
 	}								\