material: generalize how we compare simple material properties
material: generalize how we compare simple material properties

In _cogl_material_equal we were repeating the same code pattern to
compare several of the state groups so this just adds
simple_property_equal function that's now used instead.

djdeath/cogl,Distrotech/cogl,gcampax/cogl,Distrotech/cogl,djdeath/cogl,djdeath/cogl-android,Distrotech/cogl,gcampax/cogl,Distrotech/cogl,spatulasnout/cogl,collects/cogl,gcampax/cogl,spatulasnout/cogl,gcampax/cogl,collects/cogl,djdeath/cogl,djdeath/cogl-android,djdeath/cogl-android