drm/i915/selftest: Extend ctx_timestamp ICL workaround to GEN11

drm/i915/selftest: Extend ctx_timestamp ICL workaround to GEN11

EHL and JSL are also observing requirement for 80ns interval for
CTX_TIMESTAMP thus extending it to GEN11.

Changes since V1:
	- IS_GEN replaced by GRAPHICS_VER - Tvrtko

Acked-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Signed-off-by: Tejas Upadhyay <tejaskumarx.surendrakumar.upadhyay@intel.com>
Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20210624112250.895410-1-tejaskumarx.surendrakumar.upadhyay@intel.com