media: ov2740: add NVMEM interface to read customized OTP data

ov2740 includes 512bytes of one-time programmable memory and
256 bytes are reserved for customers which can be used to store
customized information. This patch provide an NVMEM interface
to support read out the customized data in OTP.

Signed-off-by: Bingbu Cao <bingbu.cao@intel.com>
Signed-off-by: Qingwu Zhang <qingwu.zhang@intel.com>
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>