Move ARM build attributes into Support

Move ARM build attributes into Support

This moves the ARM build attributes definitions and support routines into the
Support library.  The support routines simply permit the conversion of the value
to and from a string representation.

The movement is prompted in order to permit access to the constants and string
representations from readobj in order to facilitate decoding of the attributes
section.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@199575 91177308-0d34-0410-b5e6-96231b3b80d8