ARM: 8161/1: footbridge: select machine dir based on ARCH_FOOTBRIDGE

Syntactically FOOTBRIDGE and ARCH_FOOTBRIDGE are identical (the former
is defined in an if ARCH_FOOTBRIDGE block and the latter selects the
former).

Sematically FOOTBRIDGE means "we have a DC21285 (aka footbridge) device
in the system" and ARCH_FOOTBRIDGE is the support for boards with a
footbridge device, so ARCH_FOOTBRIDGE is the better symbol here.

Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>