RISC-V: Move riscv_insn_is_* macros into a common header

Right now the riscv kernel has (at least) two independent sets
of functions to check if an encoded instruction is of a specific
type. One in kgdb and one kprobes simulate-insn code.

More parts of the kernel will probably need this in the future,
so instead of allowing this duplication to go on further,
move macros that do the function declaration in a common header,
similar to at least aarch64.

Reviewed-by: Conor Dooley <conor.dooley@microchip.com>
Reviewed-by: Andrew Jones <ajones@ventanamicro.com>
Reviewed-by: Lad Prabhakar <prabhakar.mahadev-lad.rj@bp.renesas.com>
Signed-off-by: Heiko Stuebner <heiko.stuebner@vrull.eu>
Link: https://lore.kernel.org/r/20221223221332.4127602-7-heiko@sntech.de
Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>