RISC-V: Reorganize testcases for CFI directives

This commit reorganizes and adds some CSRs to csr-dw-regnums.[sd] to
make it test the same CSRs as csr.s.

gas/ChangeLog:

	* testsuite/gas/riscv/csr-dw-regnums.s: Reorganize and add
	defined CSRs tested in csr.s.
	* testsuite/gas/riscv/csr-dw-regnums.d: Likewise.