st/mesa: Enable the ARB_shading_language_420pack extension for 1.30+.
st/mesa: Enable the ARB_shading_language_420pack extension for 1.30+.

Any driver that supports GLSL 1.30 should be able to handle this
extension, as it's entirely implemented in the GLSL compiler.

Signed-off-by: Kenneth Graunke <bd2562f754ec92342f93f61c25d731e290a2ffa8@whitecape.org>
Reviewed-by: Marek Olšák <74bac9a67a04041c3586cda013cc5a11352e67be@gmail.com>

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