mesa/st: enable ARB_gpu_shader5 if the reported GLSL version >= 400
mesa/st: enable ARB_gpu_shader5 if the reported GLSL version >= 400

The ARB_gpu_shader5 extension is made up of a lot of small sub-parts.
Instead of adding PIPE_CAP's for each of these, just rely on the GLSL
version reported by the pipe driver. The remaining extensions lend
themselves naturally to being checked through a single CAP.

Signed-off-by: Ilia Mirkin <bcbbb7aa705ec3a5fc5824c01a845186c3d62fca@alum.mit.edu>
Reviewed-by: Marek Olšák <8c7344a1abdb103e79ecfd488098373070c3c70e@amd.com>

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