st/dri: Don't require a dri_format for image creation.

st/dri: Don't require a dri_format for image creation.

Nothing in EGL_KHR_gl_image.txt seems to let us deny creation based on
formats, and doing so causes many failures in
dEQP-EGL.functional.image.api.*

The NONE value we were protecting from only gets looked at in the
__DRI_IMAGE_ATTRIB_FORMAT and __DRI_IMAGE_ATTRIB_FOURCC queries, which are
used from wayland and gbm (which throw an error cleanly on unknown format)
and DMABUF export.

Reviewed-by: Marek Olšák <marek.olsak@amd.com>