drm/i915/gen11: fix the SAGV block time for gen11

It's 10us for gen 11.

Reviewed-by: Mahesh Kumar <mahesh1.kumar@intel.com>
Reviewed-by: James Ausmus <james.ausmus@intel.com>
Signed-off-by: Paulo Zanoni <paulo.r.zanoni@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180130134918.32283-7-paulo.r.zanoni@intel.com