glsl/gs: Prevent illegal input/output primitive types.

From the GLSL 1.50 spec, section 4.3.8.1 (Input Layout Qualifiers):

    The layout qualifier identifiers for geometry shader inputs are

        layout-qualifier-id
            points
            lines
            lines_adjacency
            triangles
            triangles_adjacency

And from section 4.3.8.2 (Output Layout Qualifiers)

    The layout qualifier identifiers for geometry shader outputs are

        layout-qualifier-id
            points
            line_strip
            triangle_strip
            max_vertices = integer-constant

We were erroneously allowing line_strip and triangle_strip to be used
as input qualifiers, and we were allowing lines, lines_adjacency,
triangles, and triangles_adjacency to be used as output qualifiers.

Fixes piglit tests "glsl-1.50-gs-{input,output}-layout-qualifiers *".