i965: remove scaling factors from P010, P012

i965: remove scaling factors from P010, P012

Patch removes scaling factors introduced in 2a2e69f975b but leaves
option to use scaling in place as it could be useful with other upcoming
YUV formats.

We did this scaling because ffmpeg was shifting channel bits down, however
it seems this is not the right place as compositor wants to flip same
buffers directly to display as well and therefore bitshifting needs to be
done by the client when receiving frame from ffmpeg.

Now P0x formats are treated the same, e.g. P010 is same as P016 but with
lower 6 bits set to zeros.

Fixes: 2a2e69f975b "i965: add P0x formats and propagate required scaling factors"
Signed-off-by: Tapani Pälli <tapani.palli@intel.com>
Reviewed-by: Lionel Landwerlin <lionel.g.landwerlin@intel.com>