[ARM] Change CRC predicate to just HasCRC

This removes the backend requirement for crc instructions on HasV8, relying on
just HasCRC instead. This should allow them to be selected with ArmV7 + crc,
making them more usable whilst hopefully not making them incorrectly generated
(they only come from intrinsics, and HasCRC usually requires HasV8). This is
how most other instructions are specified.