mailbox: llce: Introduce a new category of commands

commit 97855f469e1df5b46c0fba769516b83866574476 from
https://github.com/nxp-auto-linux/linux



Software commands do not need interaction with the firmware and can be
resolved at the level of the mailbox driver. One such example is
obtaining the FIFO number associated with a hardware controller.

Issue: ALB-9835
Signed-off-by: Ghennadi Procopciuc <ghennadi.procopciuc@nxp.com>
Signed-off-by: Zhantao Tang <zhantao.tang@windriver.com>