microblaze: Fix ASM optimized code for LE

Microblaze little-endian doesn't support ASM optimized library
functions(memcpy/memmove). Kconfig doens't contain
any information about endian that's why it is necessary to
check it in the source code.
The code is used with barrel shifter is used.
Signed-off-by: Michal Simek <monstr@monstr.eu>

arch/microblaze/lib/fastcopy.S

@@ -29,6 +29,10 @@
  *	between mem locations with size of xfer spec'd in bytes
  */
 
+#ifdef __MICROBLAZEEL__
+#error Microblaze LE not support ASM optimized lib func. Disable OPT_LIB_ASM.
+#endif
+
 #include <linux/linkage.h>
 	.text
 	.globl	memcpy