glsl: double support for uniform buffer objects

Signed-off-by: Tapani Pälli <tapani.palli@intel.com>
glsl: support double in 420pack vector constructor

Patch adds conversion support for when constructing a dvec from
items of a different type.

Signed-off-by: Tapani Pälli <tapani.palli@intel.com>
glsl: set correct size for double array uniforms

+ fix initializer bug in double array uniforms

(merge these to Dave's 'glsl: add double support')

Signed-off-by: Tapani Pälli <tapani.palli@intel.com>