RISC-V: Replace .option rvc/norvc with .option arch, +c/-c.

RISC-V: Replace .option rvc/norvc with .option arch, +c/-c.

Since the .option rvc/norvc directives are obsolete, replace them with
the new proposed diretives: .option arch, +c/-c.  And also reset the
riscv_opts.rvc flag for the .option arch directives.

gas/
	* config/tc-riscv.c (s_riscv_option): Reset the riscv_opts.rvc
	for the .option arch directives.
	* testsuite/gas/riscv/align-1.s: Replace the obsolete .option
	rvc/norvc with .option arch, +c/-c.
	* testsuite/gas/riscv/c-add-addi.s: Likewise.
	* testsuite/gas/riscv/c-nonzero-imm.s: Likewise.
	* testsuite/gas/riscv/c-nonzero-reg.s: Likewise.
	* testsuite/gas/riscv/c-zero-imm-64.s: Likewise.
	* testsuite/gas/riscv/c-zero-imm.s: Likewise.
	* testsuite/gas/riscv/c-zero-reg.s: Likewise.
	* testsuite/gas/riscv/ext.s: Likewise.
	* testsuite/gas/riscv/mapping-01.s: Likewise.
	* testsuite/gas/riscv/mapping-02.s: Likewise.
	* testsuite/gas/riscv/mapping-03.s: Likewise.
	* testsuite/gas/riscv/mapping-04.s: Likewise.
	* testsuite/gas/riscv/no-relax-align-2.s: Likewise.
	* testsuite/gas/riscv/shamt-32.s: Likewise.
	* testsuite/gas/riscv/shamt-64.s: Likewise.