frontend/va: Remove duplicate code in format support checking/reporting.

frontend/va: Remove duplicate code in format support checking/reporting.

In config.c there are multiple copies of the code checking for VA_FORMAT_RT_*, this can lead
to confusion and is hard to maintain without knowing to change the code in all the places.

This commit extracts out the duplicated code into a function that checks format support
for a given profile and entrypoint, then this function is called from several places that
had the copies of this code in vlVaCreateConfig/vlVaGetConfigAttributes.

Please also note that after this change, all entrypoints/profiles will be checked for all
formats in the pipe_screen: YUV420/YUV420_10/YUV422/RGB32/YUV400/YUV444

Acked-by: Ruijing Dong <ruijing.dong@amd.com>
Tested-by: Sathishkumar S <sathishkumar.sundararaju@amd.com>
Reviewed-by: Jesse Natalie <jenatali@microsoft.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/21466>