[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.

(cherry picked from commit a82c106e)