glsl: couple shader_enums cleanups

Add missing enum to gl_system_value_name() and move VARYING_SLOT_MAX /
FRAG_RESULT_MAX / etc into shader_enums.h as suggested by Emil.

v2: add STATIC_ASSERT()'s

Reported-by: Emil Velikov <emil.l.velikov@gmail.com>
Acked-by: Emil Velikov <emil.velikov@collabora.com>
Reviewed-by: Jason Ekstrand <jason@jlekstrand.net>
Signed-off-by: Rob Clark <robclark@freedesktop.org>
3 files changed