cogl: Use pixel_format_to_gl_with_target on bitmap uploading paths

We already do have a texture with an internal format in these paths,
so we should check the required format according to it.

This fixes CoglAtlasTexture (and CoglPangoRenderer indirectly), as
it forces a RGBA format on its texture, but pixel_format_to_gl()
anyway assumed swizzling is performed on the texture, while it is
not the case.

https://bugzilla.gnome.org/show_bug.cgi?id=779234