[AArch64] Implement Clang CLI interface proposal about "-march".

1. Revert "Add default feature for CPUs on AArch64 target in Clang"
at r210625. Then, all enabled feature will by passed explicitly by
-target-feature in -cc1 option.

2. Get "-mfpu" deprecated.

3. Implement support of "-march". Usage is:
    -march=armv8-a+[no]feature
  For instance, "-march=armv8-a+neon+crc+nocrypto". Here "armv8-a" is
  necessary, and CPU names are not acceptable. Candidate features are
  fp, neon, crc and crypto. Where conflicting feature modifiers are
  specified, the right-most feature is used.

4. Implement support of "-mtune". Usage is:
    -march=CPU_NAME
  For instance, "-march=cortex-a57". This option will ONLY get
  micro-architectural feature enabled specifying to target CPU,
  like "+zcm" and "+zcz" for cyclone. Any architectural features
  WON'T be modified.

5. Change usage of "-mcpu" to "-mcpu=CPU_NAME+[no]feature", which is
  an alias to "-march={feature of CPU_NAME}+[no]feature" and
  "-mtune=CPU_NAME" together. Where this option is used in conjunction
  with -march or -mtune, those options take precedence over the
  appropriate part of this option.

llvm-svn: 213353