[MIPS] Fast android_memset for Mips64, Mipsr6

Fix broken mips64 build by replacing mips32r2-only android_memset.S.
Use HW-bonded pairs of 64-bit stores to fill 128 bits/cycle.
Rely on HW automatic cache prefetch optimizations.
Software cache prefetching is counterproductive on next mips cores.
New method is coded in C, and also works okay on non-Mips architectures.

Change-Id: Id7153a8fe11538fe25287e101375661b0e99e2a2
diff --git a/libcutils/Android.mk b/libcutils/Android.mk
index c636196..9dc15d1 100644
--- a/libcutils/Android.mk
+++ b/libcutils/Android.mk
@@ -111,8 +111,9 @@
 
 LOCAL_SRC_FILES_arm += arch-arm/memset32.S
 LOCAL_SRC_FILES_arm64 += arch-arm64/android_memset.S
-LOCAL_SRC_FILES_mips += arch-mips/android_memset.S
-LOCAL_SRC_FILES_mips64 += arch-mips/android_memset.S
+
+LOCAL_SRC_FILES_mips += arch-mips/android_memset.c
+LOCAL_SRC_FILES_mips64 += arch-mips/android_memset.c
 
 LOCAL_SRC_FILES_x86 += \
         arch-x86/android_memset16.S \