Blackfin: export the last exception cause via debugfs

We have some test code that runs in userspace that exercises the exception
handling of the Blackfin pretty thoroughly.  Part of the validation process
is checking the exact exception triggered, so export the last one seen to
userspace via debugfs when debugging is enabled for the test code to check.

Signed-off-by: Robin Getz <robin.getz@analog.com>
Signed-off-by: Mike Frysinger <vapier@gentoo.org>

arch/blackfin/kernel/traps.c

@@ -68,6 +68,13 @@
 	({ if (0) printk(fmt, ##arg); 0; })
 #endif
 
+#if defined(CONFIG_DEBUG_MMRS) || defined(CONFIG_DEBUG_MMRS_MODULE)
+u32 last_seqstat;
+#ifdef CONFIG_DEBUG_MMRS_MODULE
+EXPORT_SYMBOL(last_seqstat);
+#endif
+#endif
+
 /* Initiate the event table handler */
 void __init trap_init(void)
 {
@@ -245,6 +252,9 @@ asmlinkage void trap_c(struct pt_regs *fp)
 	unsigned long trapnr = fp->seqstat & SEQSTAT_EXCAUSE;
 
 	trace_buffer_save(j);
+#if defined(CONFIG_DEBUG_MMRS) || defined(CONFIG_DEBUG_MMRS_MODULE)
+	last_seqstat = (u32)fp->seqstat;
+#endif
 
 	/* Important - be very careful dereferncing pointers - will lead to
 	 * double faults if the stack has become corrupt