glsl/types: Make subroutine types have a single matrix column

glsl/types: Make subroutine types have a single matrix column

That way, if we do the usual thing of multiplying vector_elements by
matrix_columns we get the actual number of components in the type as per
component_slots().

While we're at it, we also switch to using the actual C++ field
initializers for vector_elements and matrix_columns.

Reviewed-by: Dave Airlie <airlied@redhat.com>
Reviewed-by: Iago Toral Quiroga <itoral@igalia.com>