drm/i915/gen9+: Fix initial readout for Y tiled framebuffers

drm/i915/gen9+: Fix initial readout for Y tiled framebuffers

If BIOS configured a Y tiled FB we failed to set up the backing object
tiling accordingly, leading to a lack of GT fence installed and a
garbled console.

The problem was bisected to
commit 011f22eb545a ("drm/i915: Do NOT skip the first 4k of stolen memory for pre-allocated buffers v2")
but it just revealed a pre-existing issue.

Kudos to Ville who suspected a missing fence looking at the corruption
on the screen.

Cc: Ville Syrjälä <[email protected]>
Cc: Mika Westerberg <[email protected]>
Cc: Hans de Goede <[email protected]>
Cc: <[email protected]>
Cc: <[email protected]>
Reported-by: Mika Westerberg <[email protected]>
Reported-by: <[email protected]>
Tested-by: <[email protected]>
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=108264
Fixes: bc8d7dffacb1 ("drm/i915/skl: Provide a Skylake version of get_plane_config()")
Signed-off-by: Imre Deak <[email protected]>
Reviewed-by: Ville Syrjälä <[email protected]>
Link: https://patchwork.freedesktop.org/patch/msgid/[email protected]
(cherry picked from commit 914a4fd8cd28016038ce749a818a836124a8d270)
Signed-off-by: Rodrigo Vivi <[email protected]>