For windowed mode:
* It doesn't matter if there are no adapter modes for the display format.
* A backbuffer format is valid so long as there's support for color conversion
 to the display format.
* A backbuffer format of D3DFMT_UNKNOWN is allowed and means that it should be
 the same as the display format.

d3d9: Make CheckDeviceType() fail for display formats other than D3DFMT_X8R8G8B8 and D3DFMT_R5G6B5 in full-screen.

The adapter mode functions already enforce this, and tests show
CheckDeviceType() should fail for full-screen mode with display formats for
which there are no adapter modes.