ARM: mxs: Add reset routines

 - The mxs wdog is implemented in RTC block.
 - There is a generic software reset routine for most modules on mxs.

Signed-off-by: Shawn Guo <shawn.guo@freescale.com>
Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>