[2/7] d3dx9: Add a utility function for retrieving information about a pixel format

[Tony Wasserka]

Used to create things like color masks & shifts in a more comfortable
way without having to do a bunch of switches covering every format.
The format table will be expanded whenever there's support for a new
format in D3DXLoadsurfaceFromMemory.
This function will be used in D3DXCheckTextureRequirements, too.