main: Fix MaxUniformComponents for geometry shaders.

For both vertex and fragment shaders we default MaxUniformComponents
to 4 * MAX_UNIFORMS.  It makes sense to do this for geometry shaders
too; if back-ends have different limits they can override them as
necessary.

Fixes piglit test:
spec/glsl-1.50/built-in constants/gl_MaxGeometryUniformComponents

Cc: "10.0" <mesa-stable@lists.freedesktop.org>