platform/x86: mlx-platform: Add COME board revision register

platform/x86: mlx-platform: Add COME board revision register

Extend COME CPLD with board configuration register for getting board
revision. The value of this register is pushed by hardware through GPIO
pins.
The purpose of it is to expose some minor BOM changes.

Signed-off-by: Vadim Pasternak <vadimp@nvidia.com>
Reviewed-by: Oleksandr Shamray <oleksandrs@nvidia.com>
Link: https://lore.kernel.org/r/20220711084559.62447-7-vadimp@nvidia.com
Reviewed-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Hans de Goede <hdegoede@redhat.com>