xtensa: nommu: don't build most of the cache flushing code

Most cache flushing code is only relevant for MMU. Don't build it for
nommu configuration.

Signed-off-by: Max Filippov <jcmvbkbc@gmail.com>

arch/xtensa/mm/Makefile

@@ -2,6 +2,6 @@
 # Makefile for the Linux/Xtensa-specific parts of the memory manager.
 #
 
-obj-y			:= init.o cache.o misc.o
-obj-$(CONFIG_MMU)	+= fault.o mmu.o tlb.o
+obj-y			:= init.o misc.o
+obj-$(CONFIG_MMU)	+= cache.o fault.o mmu.o tlb.o
 obj-$(CONFIG_HIGHMEM)	+= highmem.o