rsi: add common structures needed for command packets

All internal management packets (command packets) use some common
fields and some packet specific fields for packet descriptors.
This patch adds some common structures which are needed for all
command packets.

Signed-off-by: Prameela Rani Garnepudi <prameela.j04cs@gmail.com>
Signed-off-by: Amitkumar Karwar <amit.karwar@redpinesignals.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>