ARM: mxs: Add SanDisk Sansa Fuze+ board

Add STMP3780-based Sansa Fuze+ board. This board is a small PMP
device sporting a CPU which was later rebranded to i.MX233 .
Currently supported is USB gadget mode and MMC .

Signed-off-by: Marek Vasut <marex@denx.de>
Cc: Fabio Estevam <fabio.estevam@freescale.com>
Cc: Otavio Salvador <otavio@ossystems.com.br>
Cc: Stefano Babic <sbabic@denx.de>