mesa: Add _mesa_pack_uint_rgba_row() format conversion function

mesa: Add _mesa_pack_uint_rgba_row() format conversion function

We will use this later on to handle uint conversion scenarios in a master
convert function.

v2:
- Modify pack_uint_*() function generation to use c.datatype() and
  f.datatype().
- Remove UINT_TO_FLOAT() macro usage from pack_uint*()
- Remove "if not f.is_normalized()" conditional as pack_uint*()
  functions are only autogenerated for non normalized formats.

v3:
- Add clamping for non-normalized integer formats in pack_uint*()

Signed-off-by: Samuel Iglesias Gonsalvez <siglesias@igalia.com>
Reviewed-by: Jason Ekstrand <jason.ekstrand@intel.com>