RISC-V: Add instructions and operand set for z[fdq]inx

RISC-V: Add instructions and operand set for z[fdq]inx

Reuse float instructions in INSN_CLASS_F/D/Q, use riscv_subset_supports to
verify if z*inx enabled and use gpr instead of fpr when z*inx is enable.

bfd/ChangeLog:

* elfxx-riscv.c (riscv_multi_subset_supports): Added support for
  z*inx extension.

gas/ChangeLog:

* config/tc-riscv.c (riscv_ip): Added register choice for z*inx.

include/ChangeLog:

* opcode/riscv.h (enum riscv_insn_class): Reused INSN_CLASS_* for z*inx.

opcodes/ChangeLog:

* riscv-dis.c (riscv_disassemble_insn): Added disassemble check for
  z*inx.
* riscv-opc.c: Reused INSN_CLASS_* for z*inx.

Reviewed-by: Palmer Dabbelt <palmer@rivosinc.com>