[ARM, AArch64] Move ARM/AArch64 target parsers into

separate files to enable future changes.
    
This moves ARM and AArch64 target parsing into their
own files. They are still accessible through 
TargetParser.h as before.

Several functions in AArch64 which were just forwarders to ARM
have been removed. All except AArch64::getFPUName were unused,
and that was only used in a test. Which itself was overlapping
one in ARM, so it has also been removed.

Differential revision: https://reviews.llvm.org/D53980

llvm-svn: 347741