riscv: sbi: add Firmware Feature (FWFT) SBI extensions definitions

The Firmware Features extension (FWFT) was added as part of the SBI 3.0
specification. Add SBI definitions to use this extension.

Signed-off-by: Clément Léger <cleger@rivosinc.com>
Reviewed-by: Samuel Holland <samuel.holland@sifive.com>
Tested-by: Samuel Holland <samuel.holland@sifive.com>
Reviewed-by: Deepak Gupta <debug@rivosinc.com>
Reviewed-by: Andrew Jones <ajones@ventanamicro.com>
Reviewed-by: Atish Patra <atishp@rivosinc.com>
Link: https://lore.kernel.org/r/20250523101932.1594077-2-cleger@rivosinc.com


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