firmware: octeontx2: sysfs interface for retimer

commit b6b24543b47c0ee0ab25fa7d58a7a15b8dedb1e9 from
git@git.assembla.com:cavium/WindRiver.linux.git

Added sysfs interface providing basic control
over Retimer device for cnf10kb platform.
Each of the four devices will expose simple
interface for setting GSERM index that is to be
routed through the MUX and the ethernet mode -
- both effective from the next boot.

Signed-off-by: Damian Eppel <deppel@marvell.com>
Change-Id: I142f01da6dc390f75dd114958f406bc3923b014a
Reviewed-on: https://sj1git1.cavium.com/c/IP/SW/kernel/linux/+/100308
Reviewed-by: Chandrakala Chavva <cchavva@marvell.com>
Tested-by: sa_ip-sw-jenkins <sa_ip-sw-jenkins@marvell.com>
Signed-off-by: Ruiqiang Hao <Ruiqiang.Hao@windriver.com>