RISC-V: Support the INSN_CLASS.*F.* classes for .insn directive.

RISC-V: Support the INSN_CLASS.*F.* classes for .insn directive.

We have to enable the f extension through -march or ELF attribute if we use the
FPR in .insn directive.  The behavior is same as the riscv_opcodes.

	2019-11-12  Nelson Chu  <nelson.chu@sifive.com>
	opcodes/
	* riscv-opc.c (riscv_insn_types): Replace the INSN_CLASS_I with
	INSN_CLASS_F and the INSN_CLASS_C with INSN_CLASS_F_AND_C if we
	use the floating point register (FPR).

	gas/
	* testsuite/gas/riscv/insn.d: Add the f extension to -march option.

Change-Id: I4f59d04c82673ef84c56ecd2659ad8ce164dd626