video: tegra: camera: export symbols for VI module

video: tegra: camera: export symbols for VI module

If VI driver is built as a module, it needs some symbols from tegra
camera driver.

It also fixed some errors when we unload VI driver module:
 - remove debugfs entry
 - unregister misc device driver
 - release regulator
 - release mutex lock when tegra_camera_powergate_init() fails

Bug 1240806

Change-Id: Ie0a2718d96a80c2bd0c2cc441763593753fe8bea
Signed-off-by: Bryan Wu <pengw@nvidia.com>
Reviewed-on: http://git-master/r/256967
Reviewed-by: Automatic_Commit_Validation_User
Reviewed-by: Terje Bergstrom <tbergstrom@nvidia.com>
Reviewed-by: Allen Martin <amartin@nvidia.com>