mainboard: Remove commented include lines for mc146818rtc.h

Change-Id: I4d830d988b74f2403ef8979cbafcaee3018fea62
Signed-off-by: Edward O'Callaghan <eocallaghan@alterapraxis.com>
Reviewed-on: http://review.coreboot.org/7423
Reviewed-by: Marc Jones <marc.jones@se-eng.com>
Tested-by: build bot (Jenkins)