Nook camera stub (1/2)

Showing photospheres in Google+ on ovation (maybe hummingbird too)
causes an FC.  Log indicates that camera HAL is being queried.
Apparently USE_CAMERA_STUB is no longer sufficient, so this
implements a simple camera stub for g+.  Testing with other apps
that use the camera seems to have no ill effects or FC's
(verified via logcat).

Requires BN_CAMERA_STUB definition in ovation device tree.

Change-Id: Ib361d90f6c7e22450fd5d33164a24367714eed0f