[Libva] JPEG decoding API

[Gwenole Beauchesne]

Hi,

I would suggest the following changes:

1. Remove the VA_JPEG_ROTATION_* definitions. They are the same as the
current VA_ROTATION_* definitions used as display attributes. Besides,
even if they were not, we could still use them an remap accordingly in
the driver.

2. s/count_in_mcus/num_mcus/ to retain the num_* coding style?

3. Is there a reason not to make slice params components[] refer to
the component ids directly?

Thanks,
Gwenole.