RISC-V: PR33216, Fixed gcc testcases failed for commit 28520d7

RISC-V: PR33216, Fixed gcc testcases failed for commit 28520d7

I made a stupid mistake in the commit 28520d7, allow to assemble slli/srli/srai
with 0 immediate to hint c.slli/c.srli/c.srai.  These hints will be regared as
illegal instruction for gdb and qemu, so at least I got following gcc testcases
failed,

                === g++: Unexpected fails for rv64gc lp64d medlow ===
FAIL: c-c++-common/torture/builtin-arith-overflow-17.c   -O0  execution test
FAIL: c-c++-common/torture/builtin-arith-overflow-6.c   -O0  execution test
FAIL: c-c++-common/torture/builtin-arith-overflow-p-17.c   -O0  execution test
FAIL: c-c++-common/torture/builtin-arith-overflow-p-6.c   -O0  execution test

                === gfortran: Unexpected fails for rv64gc lp64d medlow ===
FAIL: gfortran.dg/leadz_trailz_2.f90   -O0  execution test

                === gcc: Unexpected fails for rv64gc lp64d medlow ===
FAIL: c-c++-common/torture/builtin-arith-overflow-17.c   -O0  execution test
FAIL: c-c++-common/torture/builtin-arith-overflow-6.c   -O0  execution test
FAIL: c-c++-common/torture/builtin-arith-overflow-p-17.c   -O0  execution test
FAIL: c-c++-common/torture/builtin-arith-overflow-p-6.c   -O0  execution test

So we should just allow c.slli/c.srli/c.srai with zero immediate as hints, but
don't allow slli/srli/srai with zero immediate.

gas/
	PR 33216
	* testsuite/gas/riscv/c-zero-imm.d: Only allow c.slli/c.srli/c.srai
	with zero immediate as hints, but don't allow slli/srli/srai with
	zero immediate.
	* testsuite/gas/riscv/c-zero-imm.s: Likewise.
opcodes/
	PR 33216
	* riscv-opc.c (match_slli_as_c_slli): Added back.
	(match_srxi_as_c_srxi): Likewise.
	(riscv_opcodes): Only allow c.slli/c.srli/c.srai with zero immediate
	as hints, but don't allow slli/srli/srai with zero immediate.