RISC-V: Optimze the reverse conditions of rotate shift

RISC-V: Optimze the reverse conditions of rotate shift

gcc/ChangeLog:

	* config/riscv/bitmanip.md (rotrsi3_sext): Support generating
	roriw for constant counts.
	* rtl.h (reverse_rotate_by_imm_p): Add function declartion
	* simplify-rtx.cc (reverse_rotate_by_imm_p): New function.
	(simplify_context::simplify_binary_operation_1): Use it.
	* expmed.cc (expand_shift_1): Likewise.

gcc/testsuite/ChangeLog:

	* gcc.target/riscv/zbb-rol-ror-04.c: New test.
	* gcc.target/riscv/zbb-rol-ror-05.c: New test.
	* gcc.target/riscv/zbb-rol-ror-06.c: New test.
	* gcc.target/riscv/zbb-rol-ror-07.c: New test.