wined3d: Properly check if the swapchain format is WINED3DFMT_P8_UINT in primary_render_target_is_p8().

The surface needs to be part of a swapchain to be flipped, but that doesn't
have much to do with WINED3DUSAGE_RENDERTARGET. We can just remove the check
here, because ddraw_surface7_Flip() already has the correct check.

r500 does not support anything but AMD's extension depth texture formats
on Windows 7. Plain surfaces work OK with the builtin formats.

wined3d: Replace surface_modify_location(surface, location, FALSE) calls with surface_invalidate_location().