arm64: vdso32: drop test for -march=armv8-a

As Arnd points out:
  gcc-4.8 already supported -march=armv8, and we require gcc-5.1 now, so
  both this #if/#else construct and the corresponding
  "cc32-option,-march=armv8-a" check should be obsolete now.

Link: https://lore.kernel.org/lkml/CAK8P3a3UBEJ0Py2ycz=rHfgog8g3mCOeQOwO0Gmp-iz6Uxkapg@mail.gmail.com/
Suggested-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Nick Desaulniers <ndesaulniers@google.com>
Reviewed-by: Vincenzo Frascino <vincenzo.frascino@arm.com>
Reviewed-by: Nathan Chancellor <nathan@kernel.org>
Link: https://lore.kernel.org/r/20211019223646.1146945-3-ndesaulniers@google.com
Signed-off-by: Will Deacon <will@kernel.org>

arch/arm64/include/asm/vdso/compat_barrier.h

@@ -20,16 +20,9 @@
 
 #define dmb(option) __asm__ __volatile__ ("dmb " #option : : : "memory")
 
-#if __LINUX_ARM_ARCH__ >= 8
 #define aarch32_smp_mb()	dmb(ish)
 #define aarch32_smp_rmb()	dmb(ishld)
 #define aarch32_smp_wmb()	dmb(ishst)
-#else
-#define aarch32_smp_mb()	dmb(ish)
-#define aarch32_smp_rmb()	aarch32_smp_mb()
-#define aarch32_smp_wmb()	dmb(ishst)
-#endif
-
 
 #undef smp_mb
 #undef smp_rmb

arch/arm64/kernel/vdso32/Makefile

@@ -65,13 +65,7 @@ endif
 # From arm vDSO Makefile
 VDSO_CAFLAGS += -fPIC -fno-builtin -fno-stack-protector
 VDSO_CAFLAGS += -DDISABLE_BRANCH_PROFILING
-
-
-# Try to compile for ARMv8. If the compiler is too old and doesn't support it,
-# fall back to v7. There is no easy way to check for what architecture the code
-# is being compiled, so define a macro specifying that (see arch/arm/Makefile).
-VDSO_CAFLAGS += $(call cc32-option,-march=armv8-a -D__LINUX_ARM_ARCH__=8,\
-                                   -march=armv7-a -D__LINUX_ARM_ARCH__=7)
+VDSO_CAFLAGS += -march=armv8-a
 
 VDSO_CFLAGS := $(VDSO_CAFLAGS)
 VDSO_CFLAGS += -DENABLE_COMPAT_VDSO=1