[media] it913x: get rid of script loader and and private header file

Used script loader is quite useless and hides register numbers
making code hard to understand. Get rid of it and use standard
RegMap register write functions directly.

it913x_priv.h file leaves empty after that change and is also
removed.

Signed-off-by: Antti Palosaari <crope@iki.fi>
Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>