mx6sabresd: Avoid calling setup_display() from SPL code

There is no need call setup_display() from SPL code, so move it to
board_init(), which executes only in U-Boot proper.

Reported-by: Stefano Babic <sbabic@denx.de>
Signed-off-by: Fabio Estevam <fabio.estevam@nxp.com>
Reviewed-by: Stefano Babic <sbabic@denx.de>