[mips] Add support for CRC ASE

This includes

  Instructions: crc32b, crc32h, crc32w, crc32d,
                crc32cb, crc32ch, crc32cw, crc32cd

  Assembler directives: .set crc, .set nocrc, .module crc, .module nocrc

  Attribute: crc

  .MIPS.abiflags: CRC (0x8000)

Patch by Vladimir Stefanovic.

Differential Revision: https://reviews.llvm.org/D44176

llvm-svn: 327511