RISC-V: Add missing hint instructions from RV128I.

RISC-V: Add missing hint instructions from RV128I.

	gas/
	* testsuite/gas/riscv/c-zero-imm.d: Add more tests.
	* testsuite/gas/riscv/c-zero-imm.s: Likewise.
	* testsuite/gas/riscv/c-zero-reg.d: Fix typo in test.  Add disabled
	future test for RV128 support.
	* testsuite/gas/riscv/c-zero-reg.s: Likewise.

	include/
	* opcode/riscv-opc.h (MATCH_C_SRLI64, MASK_C_SRLI64): New.
	(MATCH_C_SRAI64, MASK_C_SRAI64): New.
	(MATCH_C_SLLI64, MASK_C_SLLI64): New.

	opcodes/
	* riscv-opc.c (match_c_slli, match_slli_as_c_slli): New.
	(match_c_slli64, match_srxi_as_c_srxi): New.
	(riscv_opcodes) <slli, sll>: Use match_slli_as_c_slli.
	<srli, srl, srai, sra>: Use match_srxi_as_c_srxi.
	<c.slli, c.srli, c.srai>: Use match_s_slli.
	<c.slli64, c.srli64, c.srai64>: New.