powerpc/85xx: Remove -Wa,-me500

This caused lwsync to be converted to sync on 64-bit (on 32-bit lwsync
is generated at runtime, and so wasn't affected).  Not using lwsync
caused a significant slowdown on certain workloads.

Setting this flag for any e500-enabled build is also not friendly to
multiplatform kernels.
Signed-off-by: Scott Wood <scottwood@freescale.com>

arch/powerpc/Makefile

@@ -139,7 +139,6 @@ endif
 
 cpu-as-$(CONFIG_4xx)		+= -Wa,-m405
 cpu-as-$(CONFIG_ALTIVEC)	+= -Wa,-maltivec
-cpu-as-$(CONFIG_E500)		+= -Wa,-me500
 cpu-as-$(CONFIG_E200)		+= -Wa,-me200
 
 KBUILD_AFLAGS += $(cpu-as-y)