Camera: Add usage flag for PRIVATE ImageReader

If the PRIVATE format ImageReader doesn't have any usage flag, it will
default to ZERO_SHUTTER_LAG usage, which may not work for all
IMPLEMENTATION_DEFINED sizes.

Modify ImageReaderTest and ItsService to set a usgae flag for PRIVATE
ImageReaders so that ZERO_SHUTTER_FLAG usage isn't set.

Test: Vendor testing; ImageReaderTest#testImageReaderYuvAndPrivate
Bug: 342093976
Change-Id: Ic3c433df694f17c2f2e7f6221652e5d02194a504