uboot-imx

engicam: Move uart mux init to SPL

Since, u-boot handle fdt through uart so move the UART code
to SPL instead make it to global area.

Cc: Stefano Babic <sbabic@denx.de>
Cc: Matteo Lisi <matteo.lisi@engicam.com>
Cc: Michael Trimarchi <michael@amarulasolutions.com>
Signed-off-by: Jagan Teki <jagan@amarulasolutions.com>