superio/fintek/*: Factor out generic romstage component

The romstage of Fintek Super I/O's is identical, leading to replication
of essentially the same code prone to bitrot. Herein we consolidate the
early pre-ram UART initialisation code into fintek/common, rather we
leave the exceptions to be implemented under model/.

More precisely we provide a well documented version of early_serial.c
under fintek/common and select by way of Kconfig as a generic romstage
component to Super I/O support. We leave future Super I/O's the option
to implement `non-standard` initialisation code should such a (unlikely)
need araise. A primary advantage is that new support for romstage serial
is now trival to add. We also provide some Kconfig documentation while
here.

Change-Id: I3c62561558a62ece944a167ba302fb7076bba001
Signed-off-by: Edward O'Callaghan <eocallaghan@alterapraxis.com>
Reviewed-on: http://review.coreboot.org/5575
Tested-by: build bot (Jenkins)
Reviewed-by: Patrick Georgi <patrick@georgi-clan.de>
diff --git a/src/mainboard/jetway/pa78vm5/romstage.c b/src/mainboard/jetway/pa78vm5/romstage.c
index c082a67..044d0d8 100644
--- a/src/mainboard/jetway/pa78vm5/romstage.c
+++ b/src/mainboard/jetway/pa78vm5/romstage.c
@@ -42,6 +42,7 @@
 #include "northbridge/amd/amdfam10/reset_test.c"
 #include <console/loglevel.h>
 #include "cpu/x86/bist.h"
+#include <superio/fintek/common/fintek.h>
 #include <superio/fintek/f71863fg/f71863fg.h>
 #include <cpu/amd/mtrr.h>
 #include "northbridge/amd/amdfam10/setup_resource_map.c"
@@ -102,7 +103,7 @@
 	enable_rs780_dev8();
 	sb7xx_51xx_lpc_init();
 
-	f71863fg_enable_serial(SERIAL_DEV, CONFIG_TTYS0_BASE);
+	fintek_enable_serial(SERIAL_DEV, CONFIG_TTYS0_BASE);
 
 	console_init();