cmd: sbi: Add FWFT, MPXY extensions

cmd: sbi: Add FWFT, MPXY extensions

The SBI 3.0 specification [1] adds the following extensions:

* Firmware Features Extension
* Message Proxy Extension

Let the sbi command detect their availability.

The Firmware Features Extension is already implemented in OpenSBI.

Correct the text for the DBTR extension and move it to the same position
as in the specification.

[1] https://github.com/riscv-non-isa/riscv-sbi-doc/releases/download/vv3.0-rc1/riscv-sbi.pdf

Signed-off-by: Heinrich Schuchardt <heinrich.schuchardt@canonical.com>
Reviewed-by: Leo Yu-Chi Liang <ycliang@andestech.com>