console: support integrated 7-segment displays for POST codes

console: support integrated 7-segment displays for POST codes

Add a configuration option POST_PORT which defaults to 0x80 and
can be redefined by boards which have integrated POST displays
on another I/O port. Change post.c to output POST codes to this
port instead of 0x80 hardcoded.

Change-Id: I8f8e820f8c75641b35e7249bf622b63a3604b9f3
Signed-off-by: Christoph Grenz <christophg+cb@grenz-bonn.de>
Reviewed-on: http://review.coreboot.org/221
Tested-by: build bot (Jenkins)
Reviewed-by: Rudolf Marek <r.marek@assembler.cz>
Reviewed-by: Patrick Georgi <patrick@georgi-clan.de>