mesa: check depth, stencil formats (not depths) in glBlitFramebuffer

mesa: check depth, stencil formats (not depths) in glBlitFramebuffer

We were only comparing the number of depth and stencil bits but the
extension spec actually says the formats must match:

    The error INVALID_OPERATION is generated if BlitFramebufferEXT is
    called and <mask> includes DEPTH_BUFFER_BIT or STENCIL_BUFFER_BIT
    and the source and destination depth or stencil buffer formats do
    not match.

Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>