MIPS: microMIPS: Optimise 'memset' core library function.

Optimise 'memset' to use microMIPS instructions and/or optimisations
for binary size reduction. When the microMIPS ISA is not being used,
the library function compiles to the original binary code.

Signed-off-by: Steven J. Hill <Steven.Hill@imgtec.com>
diff --git a/arch/mips/include/asm/asm.h b/arch/mips/include/asm/asm.h
index 164a21e..879691d 100644
--- a/arch/mips/include/asm/asm.h
+++ b/arch/mips/include/asm/asm.h
@@ -296,6 +296,7 @@
 #define LONG_SUBU	subu
 #define LONG_L		lw
 #define LONG_S		sw
+#define LONG_SP		swp
 #define LONG_SLL	sll
 #define LONG_SLLV	sllv
 #define LONG_SRL	srl
@@ -318,6 +319,7 @@
 #define LONG_SUBU	dsubu
 #define LONG_L		ld
 #define LONG_S		sd
+#define LONG_SP		sdp
 #define LONG_SLL	dsll
 #define LONG_SLLV	dsllv
 #define LONG_SRL	dsrl