[RISC-V][PR target/122106] Add missing predicate on crc expanders

[RISC-V][PR target/122106] Add missing predicate on crc expanders

This is a minor bug in the CRC code for RISC-V.

Essentially in the expander we have an operand without a predicate.  So it
matches anything.  But that operand really has to be a CONST_INT.  So this
patch adds the missing predicate.  I noticed we had constraints on our
define_expand.  It doesn't hurt anything, but they're never used and can easily
get out of date, so this removes the unnecessary constraints.

Tested on riscv32-elf and riscv64-elf.  Bootstrap & regression test on the
Pioneer is in flight and should finish in the next few hours.

Pushing to the trunk once CI confirms it's OK.

	PR target/122106
gcc/
	* config/riscv/bitmanip.md (crc expanders): Add predicate for
	polynomial argument.  Drop unnecessary constraints.

gcc/testsuite/

	* gcc.target/riscv/pr122106.c: New test.