mainboard/: Avoid including early_serial.c from w83627hf

Following the reasoning of:
dbbc136 mainboard/asrock/e350m1: Avoid including early_serial.c

Change-Id: I5d729b90cf6713de2674fb00c726cd2944a3ab4e
Signed-off-by: Edward O'Callaghan <eocallaghan@alterapraxis.com>
Reviewed-on: http://review.coreboot.org/5597
Tested-by: build bot (Jenkins)
Reviewed-by: Patrick Georgi <patrick@georgi-clan.de>