watchdog: i6300esb: don't depend on X86

i6300esb is on of the watchdogs QEMU can emulate. It is also available
when emulating ARM. The driver works without problems and is quite
useful to test userspace dealing with /dev/watchdog.

Signed-off-by: Michael Olbrich <m.olbrich@pengutronix.de>
Signed-off-by: Wim Van Sebroeck <wim@iguana.be>