RISC-V: Tidy and complete testing of all architecture imply rules.

RISC-V: Tidy and complete testing of all architecture imply rules.

gas/
	* testsuite/gas/riscv/imply.s: New testcase for all imply cases.
	* testsuite/gas/riscv/imply.d: Likewise.
	* testsuite/gas/riscv/march-imply-i.s: Renamed to
	imply-zicsr-zifencei.s.
	* testsuite/gas/riscv/march-imply-i2p0-02.d: Renamed to
	imply-zicsr-zifencei-i2p0-misa-spec-2p2.d.
	* testsuite/gas/riscv/march-imply-i2p1-01.d/l: Renamed to
	imply-zicsr-zifencei-i2p1-misa-spec-20191213.d.
	* testsuite/gas/riscv/march-imply-i2p0-01.d: Removed.
	Combined into new imply testcase.
	* testsuite/gas/riscv/march-imply-i2p1-02.d: Likewise.
	* testsuite/gas/riscv/march-imply-a.d: Likewise.
	* testsuite/gas/riscv/march-imply-b.d: Likewise.
	* testsuite/gas/riscv/march-imply-f.d: Likewise.
	* testsuite/gas/riscv/march-imply-g.d: Likewise.
	* testsuite/gas/riscv/march-imply-h.d: Likewise.
	* testsuite/gas/riscv/march-imply-q.d: Likewise.
	* testsuite/gas/riscv/march-imply-smcsrind.d: Likewise.
	* testsuite/gas/riscv/march-imply-smstateen.d: Likewise.
	* testsuite/gas/riscv/march-imply-unsupported.d: Likewise.
	* testsuite/gas/riscv/march-imply-v.d: Likewise.
	* testsuite/gas/riscv/march-imply-zcd.d: Likewise.
	* testsuite/gas/riscv/march-imply-zcf.d: Likewise.