pvr: Clean up & fix sampler border color support

pvr: Clean up & fix sampler border color support

Take advantage of some vk_sampler goodness and migrate all pvr
tex_formats to map to pipe_formats in pvr_formats.c. This allows us to
get rid of all the nasty manual packing functions.

This cleanup incidentally fixes some bad swizzling that was happening
in the manual handling.

Fixes: 4a2e6284 pvr: Add support for sampler border colors
Signed-off-by: Matt Coster <matt.coster@imgtec.com>
Reviewed-by: Karmjit Mahil <Karmjit.Mahil@imgtec.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/25270>