Makefile: Add CCACHE && fix build conflicts with traps.c cacheflush.h cache-v7.S
Add CCACHE to Makefile to make secondary builds faster, this is just like enabling ccache in ROM builds.
This should "Theoretically" lessen builds times by 30 - 40%, tested it and it does make the build faster.

Cherry picking will also add the fixes from the said files(traps.c, cacheflush.h & cache-v7.S)

Signed-off-by: Jean Francis Dominique S. Mabalot <jfdsmabalot@redhat.com>

Conflicts:
	Makefile
	arch/arm/include/asm/cacheflush.h
	arch/arm/mm/cache-v7.S