MIPS: unify cache maintenance functions

Move the more developed mips32 version of the cache maintenance
functions to a common arch/mips/lib/cache.c, in order to reduce
duplication between mips32 & mips64.

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 7f9b653..d939ee6 100644
--- a/arch/mips/lib/Makefile
+++ b/arch/mips/lib/Makefile
@@ -5,6 +5,7 @@
 # SPDX-License-Identifier:	GPL-2.0+
 #
 
+obj-y	+= cache.o
 obj-y	+= io.o
 
 obj-$(CONFIG_CMD_BOOTM) += bootm.o