RISC-V: add prefix to all constants/macros in parse_asm.h

RISC-V: add prefix to all constants/macros in parse_asm.h

Some of the constants and macros already have suitable RV_, RVG_ or
RVC_ prefixes.

Extend this to the rest of the file as well, as we want to use these
things in a broader scope soon.

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/20221223221332.4127602-3-heiko@sntech.de
Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>