Teach clang driver about Cortex-A53 and Cortex-A57.

Adds some Cortex-A53 strings where they were missing before.
Cortex-A57 is entirely new to clang.

Doesn't touch code only used by Darwin, in consequence of which
one of the A53 lines has been removed.

Change-Id: I5edb58f6eae93947334787e26a8772c736de6483
llvm-svn: 193364