imx: ventana: add 'gsc wd' command for enabling and disabling GSC watchdog

imx: ventana: add 'gsc wd' command for enabling and disabling GSC watchdog

This adds information about the Gateworks System Controller to the gsc command
such as the firmware version, firmware CRC and status of the GSC watchdog
(if its enabled and if its tripped).

Additionally the 'gsc wd' command can be used to enable or disable the
watchdog with the following usage:
 gsc wd enable [30|60]
 gsc wd disable

Note that the GSC registers are battery-backed by the GSC coincell so once
eanbled, they remain enabled across power-cycles or until either the GSC
firmware has been updated or FLASH has been re-programmed by the Gateworks
JTAG adapter.

Signed-off-by: Tim Harvey <tharvey@gateworks.com>