r600: report incorrect max-vertex-attrib for GL 4.4

r600: report incorrect max-vertex-attrib for GL 4.4

OpenGL 4.4 requires a max vertex attrib of 2048 or higher, but
r600 only supports 2047. Technically, this makes it an GL4.3 GPU,
but it's currently exposing GL4.4.

To avoid regressing the GL version supported in the following
patches, let's just lie and pretend like we support 2048. Any
applications using 2048 are already broken anyway.

Signed-off-by: Erik Faye-Lund <erik.faye-lund@collabora.com>
Reviewed-by: Marek Olšák <marek.olsak@amd.com>
Reviewed-by: Ian Romanick <ian.d.romanick@intel.com>