ARM: mxs: Add low-level debug UART support

 - DEBUG_LL support, which is incompatible with multi-soc MXS image
   because of different DUART base address on MX23 and MX28
 - uncompress message support

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