drm/i915: Probe whether SAGV works on pre-icl

drm/i915: Probe whether SAGV works on pre-icl

Instead of leaving the SAGV enable/disable to the first commit
let's try to disable it first thing to see if we can do it or
not (disabling SAGV is a safe thing to at any time). This avoids
running the code in this funny intermediate state where we don't
know if SAGV is available or not.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220309164948.10671-4-ville.syrjala@linux.intel.com
Reviewed-by: Stanislav Lisovskiy <stanislav.lisovskiy@intel.com>