glsl: fix check SSBOs support for builtin functions

glsl: fix check SSBOs support for builtin functions

has_shader_storage_buffer_objects() returns true also if the OpenGL
context is 4.30 or ES 3.1.

Previously, we were saying that all atomic*() GLSL builtin functions
for SSBOs were not available when OpenGL ES 3.1 context was in use.

Fixes 48 dEQP-GLES31 tests:

dEQP-GLES31.functional.ssbo.atomic.*

Signed-off-by: Samuel Iglesias Gonsalvez <siglesias@igalia.com>
Reviewed-by: Tapani Pälli <tapani.palli@intel.com>
Reviewed-by: Iago Toral Quiroga <itoral@igalia.com>