riscv: add missing SBI extension definitions

riscv: add missing SBI extension definitions

Add the System Reset Extension and the Hart State Management Extension
definitions.

Add missing RFENCE Extension enum values.

The SBI 0.1 extension constants are needed for the sbi command. Remove
an #ifdef.

Cf. https://github.com/riscv/riscv-sbi-doc/blob/master/riscv-sbi.adoc

Signed-off-by: Heinrich Schuchardt <heinrich.schuchardt@canonical.com>
Reviewed-by: Leo Yu-Chi Liang <ycliang@andestech.com>
Reviewed-by: Sean Anderson <seanga2@gmail.com>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>