ARM: dts: mxs: Add SanDisk Sansa Fuze+ support

Add support for this small MP3 player based on STMP3780 (rev.3).
Currently supported are both external microSD and internal SD-NAND
bridge, PWM and USB gadget.

Signed-off-by: Marek Vasut <marek.vasut@gmail.com>
Cc: Fabio Estevam <fabio.estevam@nxp.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>