egl: Fix A2RGB10 platform_{device,surfaceless} PBuffer configs.

egl: Fix A2RGB10 platform_{device,surfaceless} PBuffer configs.

The __DRI_IMAGE_FORMAT_* part wants to be handled for the *101010
type formats as well. Factor out a common function for that task.
That again makes the piglit egl_ext_device_base test work again
for hardware drivers.

v2: Factor out a common function for that task.
v3: dri2_pbuffer_visuals -> dri2_pbuffer_visuals

Reviewed-by: Emil Velikov <emil.velikov@collabora.com>
Fixes: 9acb94b6236 "egl: Enable 10bpc EGLConfigs for platform_{device,surfaceless}"
Signed-off-by: Mathias Fröhlich <Mathias.Froehlich@web.de>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/3790>