arm64: Add options to disable I/D caches

Add the ability to individually disable the Instruction and
Data caches on ARM64 CPUs, by means of the SCTLR[I] and
SCTLR[C] bits. This may be useful for performance
profiling, as well as for troubleshooting potential cache
problems.

Change-Id: Ibd7fc796ddf6984c7f05dcd844432164e28bb021
Signed-off-by: Stepan Moskovchenko <stepanm@codeaurora.org>