Do not read and do not convert pixels for camera

Camera is a special citizen, it delivers buffer bits
directly (no reading required) and supports
YUV_420 (interleaved), this is the only format it
supports.

Bug: 130295800
Test: emulator -wipe-data -no-snapshot -camera-back virtualscene
Test: take photo, take video
Change-Id: I0192084d88f27235d4d1a2c0a7598cd28200bc48
Merged-In: Ib37ec0a85a48d6a6ac6bbf6b9033ffd60ac7a727
Signed-off-by: Roman Kiryanov <rkir@google.com>