drm/i915: Fix async flip with decryption and/or DPT

We're currently forgetting to set the PLANE_SURF_DECRYPT
flag in the async flip path. So if the hardware were to
latch that bit despite this being an async flip we'd start
scanning out garbage. And if it doesn't latch it then I
guess we'd just end up with a weird register value that
doesn't actually match the hardware state, which isn't
great for anyone staring at register dumps.

Similarly the async flip path also forgets to call
skl_surf_address() which means the DPT address space to
GGTT address space downshift is not being applied to
the offset. Which means we are pointing PLANE_SURF
at some random location in GGTT instead of the correct
DPT page.

So let's fix two birds with one stone and extract the
PLANE_SURF calculation from skl_program_plane() into
a small helper and use it in the async flip path as well.

Cc: Anshuman Gupta <anshuman.gupta@intel.com>
Cc: Daniele Ceraolo Spurio <daniele.ceraolospurio@intel.com>
Cc: Juston Li <juston.li@intel.com>
Cc: Rodrigo Vivi <rodrigo.vivi@intel.com>
Cc: Uma Shankar <uma.shankar@intel.com>
Cc: Karthik B S <karthik.b.s@intel.com>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20211018115030.3547-3-ville.syrjala@linux.intel.com
Reviewed-by: Stanislav Lisovskiy <stanislav.lisovskiy@intel.com>