Change createAsmParser to take a MCSubtargetInfo instead of triple,

Change createAsmParser to take a MCSubtargetInfo instead of triple,
CPU, and feature string. Parsing some asm directives can change
subtarget state (e.g. .code 16) and it must be reflected in other
modules (e.g. MCCodeEmitter). That is, the MCSubtargetInfo instance
must be shared.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@134795 91177308-0d34-0410-b5e6-96231b3b80d8