[RISC-V] Minor cleanup/improvement to bset/binv patterns

[RISC-V] Minor cleanup/improvement to bset/binv patterns

  Changes since V1:
   Whitespace fixes noted by the linter
   Missed using the iterator for the output template in
<bit_optab><mode>_mask pattern!

--

This patch introduces a bit_optab iterator that maps IOR/XOR to bset and
binv (and one day bclr if we need it).  That allows us to combine some
patterns that only differed in the RTL opcode (IOR vs XOR) and in the
name/assembly (bset vs binv).

Additionally this also allow us to use the iterator in the
bset<mode>mask and bsetidisi patterns thus potentially fixing a missed
optimization.

This has gone through my tester.  I'll wait for a verdict from
pre-commit CI before moving forward.

gcc/
	* config/riscv/bitmanip.md (<bit_optab><mode>): New unified
	pattern for bset/binv using a code iterator.
	(<bit_optab>i<mode>): Likewise.
	(<bit_optab><mode>_mask): Likewise.  Support XOR via any_or.
	(<bit_optab>isidi): Likewise.
	* config/riscv/iterators.md (bit_optab): New iterator.