RISC-V: insn-def: Add I-type insn-def

CBO instructions use the I-type of instruction format where
the immediate is used to identify the CBO instruction type.
Add I-type instruction encoding support to insn-def.

Signed-off-by: Andrew Jones <ajones@ventanamicro.com>
Reviewed-by: Conor Dooley <conor.dooley@microchip.com>
Reviewed-by: Heiko Stuebner <heiko@sntech.de>
Signed-off-by: Conor Dooley <conor.dooley@microchip.com>
Reviewed-by: Andrew Jones <ajones@ventanamicro.com>
Link: https://lore.kernel.org/r/20230108163356.3063839-2-conor@kernel.org


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