drm/i915: Rework SAGV block time probing

I'd like to see the SAGV block time we got from the mailbox
in the logs regardless of whether other factors prevent the
use of SAGV.

So let's adjust the code to always query the SAGV block time,
log it, and then reset it if SAGV is not actually supported.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220309164948.10671-3-ville.syrjala@linux.intel.com


Reviewed-by: Stanislav Lisovskiy <stanislav.lisovskiy@intel.com>