[to-be-committed][RISC-V] Reassociate constants in logical ops

[to-be-committed][RISC-V] Reassociate constants in logical ops

This patch from Lyut will reassociate operands when we have shifted logical
operations.  This can simplify a constant that may not be fit in a simm12 into
a form that does fit into a simm12.

The basic work was done by Lyut.  I generalized it to handle XOR/OR.

It stands on its own, but also helps the upcoming Zbkb work from Lyut.

This has survived Ventana's CI system as well as my tester.  Obviously I'll
wait for a verdict from the Rivos CI system before moving forward.

gcc/

	* config/riscv/riscv.md (<optab>_shift_reverse<X:mode>): New pattern.

gcc/testsuite

	* gcc.target/riscv/and-shift32.c: New test.
	* gcc.target/riscv/and-shift64.c: New test.

	Co-authored-by: Jeffrey A Law <jlaw@ventanamicro.com>