RISC-V: rename parse_asm.h to insn.h

The current parse_asm header should become a more centralized place
for everything concerning parsing and constructing instructions.

We already have a header insn-def.h similar to aarch64, so rename
parse_asm.h to insn.h (again similar to aarch64) to show that it's
meant for more than simple instruction parsing.

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/20221223221332.4127602-8-heiko@sntech.de


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