POST card display support

[Jaghathiswari Rankappagounder Natarajan]

Platform driver in patch 1/3 periodically updates the most current POST code
from either the BMC or host to the POST card display.
The POST card hardware assumed is 74HC164 wired to two 7-segment displays.

(to get POST codes from bmc) On BMC state change, the character driver in
patch 2/3 is the interface to which the systemd (in openbmc) will write the
POST codes. When a new POST code is written to the character device,
the update_postcode function in patch 1/3 is called to update the post code.

(to get POST codes from host) When the host writes to port80, the lpc driver can
directly call update_postcode function in patch 1/3 to update the POST code
(will be written after lpc driver is finished);

patch 3/3 has devicetree info for controlling the POST card hardware on zaius