ARM: mxs: move mxs_get_ocotp() into mach-mxs.c

All the users of mxs_get_ocotp() are in mach-mxs.c.  Move the function
into mach-mxs.c, make it a static function, and then remove ocotp.c.

Signed-off-by: Shawn Guo <shawn.guo@linaro.org>