glsl: Parse interface array size

glsl: Parse interface array size

The size is parsed and stored in the AST, but it is not used yet.
Processing of the array size is added in the patch "glsl: Handle
instance array declarations"

v2: Update the commit message (suggested by Carl Worth).  Add a comment
to ast_uniform_block::array_size (suggested by Paul Berry).

Signed-off-by: Ian Romanick <ian.d.romanick@intel.com>
Reviewed-by: Chad Versace <chad.versace@linux.intel.com>
Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>