i.MX28: Shut down the LCD controller to avoid BootROM sampling bug

If there's some traffic on the LCD controller pads, the BootROM has trouble with
sampling the bootmode from these pads. The BootROM usually ends in a loop.

Signed-off-by: Marek Vasut <marek.vasut@gmail.com>
Cc: Chen Peter-B29397 <B29397@freescale.com>
Cc: Detlev Zundel <dzu@denx.de>
Cc: Fabio Estevam <festevam@gmail.com>
Cc: Li Frank-B20596 <B20596@freescale.com>
Cc: Lin Tony-B19295 <B19295@freescale.com>
Cc: Linux FBDEV <linux-fbdev@vger.kernel.org>
Cc: Sascha Hauer <s.hauer@pengutronix.de>
Cc: Shawn Guo <shawn.guo@freescale.com>
Cc: Stefano Babic <sbabic@denx.de>
Cc: Subodh Nijsure <snijsure@grid-net.com>
Cc: Tony Lin <tony.lin@freescale.com>
Acked-by: Shawn Guo <shawn.guo@linaro.org>
Acked-by: Wolfgang Denk <wd@denx.de>
Acked-by: Wolfram Sang <w.sang@pengutronix.de>
Tested-by: Wolfgang Denk <wd@denx.de>
Signed-off-by: Florian Tobias Schandinat <FlorianSchandinat@gmx.de>