Revert wrong removal of nand_init and nand_deselect

The manual resolution in commit ec7023db wrongly removed functions
nand_init and nand_deselect from file drivers/mtd/nand/mxc_nand_spl.c.
Revert this removal.

Signed-off-by: Albert ARIBAUD <albert.u.boot@aribaud.net>
Acked-by: Stefano Babic <sbabic@denx.de>