ENGR00275034-3 camera: ov5640: port the driver from 3.5.7

ENGR00275034-3 camera: ov5640: port the driver from 3.5.7

from commit 9293d3aaef4886eae9a500f0dabdcd2b679422b4
and commit cb1d78fc935fa00be03ae1a7b66477ad518a09dc, branch imx_3.5.7

This patch also does
- use module_i2c_driver() instead of module_init/exit.
- set the regulator reference pointer to NULL if it's not found in DT.
  Otherwise call regulator_enable/disable() on it will cause dump
  since the codes only check the regulator against NULL before the call
  and it's not NULL but still invalid.
- drop gpo regulator definition and operations since it's of no use

Signed-off-by: Robby Cai <R63905@freescale.com>