Use shared gpio code from common folder.
Bd82x6x's gpio.c and gpio.h is used by other southbridges
as well and will be removed once it is unused.
Change-Id: I8bd981c4696c174152cf41caefa6c083650d283a
Signed-off-by: Patrick Rudolph <siro@das-labor.org>
Reviewed-on: https://review.coreboot.org/13614
Tested-by: build bot (Jenkins)
Reviewed-by: Martin Roth <martinroth@google.com>