Make the "Reducing compressed framebufer size" message be DRM_INFO_ONCE()

This was sort of annoying me:

random:~$ dmesg | tail -1
[523884.039227] [drm] Reducing the compressed framebuffer size. This may lead to less power savings than a non-reduced-size. Try to increase stolen memory size if available in BIOS.
random:~$ dmesg | grep -c "Reducing the compressed"
47

This patch makes it DRM_INFO_ONCE() just like the similar message
farther down in that function is pr_info_once().

Cc: stable@vger.kernel.org
Signed-off-by: Peter Jones <pjones@redhat.com>
Acked-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Closes: https://gitlab.freedesktop.org/drm/intel/-/issues/1745
Link: https://patchwork.freedesktop.org/patch/msgid/20180706190424.29194-1-pjones@redhat.com
[vsyrjala: Rebase due to per-device logging]
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>