MIPS: unify cache initialization code

The mips32 & mips64 cache initialization code differs only in that the
mips32 code supports reading the cache size from coprocessor 0 registers
at runtime. Move the more developed mips32 version to a common
arch/mips/lib/cache_init.S & remove the now-redundant mips64 version in
order to reduce duplication. The temporary registers used are shuffled
slightly in order to work for both mips32 & mips64 builds. The RA
register is defined differently to suit mips32 & mips64, but will be
removed by a later commit in the series after further cleanup.

Signed-off-by: Paul Burton <paul.burton@imgtec.com>
Cc: Daniel Schwierzeck <daniel.schwierzeck@gmail.com>
diff --git a/arch/mips/lib/Makefile b/arch/mips/lib/Makefile
index d939ee6..ac536da 100644
--- a/arch/mips/lib/Makefile
+++ b/arch/mips/lib/Makefile
@@ -6,6 +6,7 @@
 #
 
 obj-y	+= cache.o
+obj-y	+= cache_init.o
 obj-y	+= io.o
 
 obj-$(CONFIG_CMD_BOOTM) += bootm.o