arm64: Add BTAC/LinkStack sanitizations for Kryo

Kryo cores are exposed to two vulnerabilities due to subroutine
return (called LINK-STACK) and branch target predictors.
These two issues can be mitigated through software workarounds.

Kernel:
 - Apply LINK-STACK mitigation which is issue 16 nested BL instructions
   on process context switch 'cpu_do_switch_mm()' where ASID changes.
 - Apply psci based branch predictor invalidation.

Change-Id: I983a12dabcd45e3ec757732a44fc567c12228d8b
Signed-off-by: Neeraj Upadhyay <neeraju@codeaurora.org>