drm/i915: Split current joiner hw state readout

drm/i915: Split current joiner hw state readout

We need to add a new sanity checks and also do
some preparations for adding ultrajoiner hw state readout.
Lets first split reading of the uncompressed joiner and bigjoiner
bit masks into separate functions.

v2: Fixed checkpatch warnings (Ankit)
v3: Use struct intel_display in the new functions. (Ankit)
v4: Use check for bigjoiner before reading the regs. (Ville)

Signed-off-by: Stanislav Lisovskiy <stanislav.lisovskiy@intel.com>
Signed-off-by: Ankit Nautiyal <ankit.k.nautiyal@intel.com>
Reviewed-by: Suraj Kandpal <suraj.kandpal@intel.com>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240930163549.416410-2-ankit.k.nautiyal@intel.com