drm/i915/icl: update ddb entry start/end mask during hw ddb readout

Gen11/ICL onward ddb entry start/end mask is increased from 10 bits to
11 bits. This patch make changes to use proper mask for ICL+ during
hardware ddb value readout.

Changes since V1:
 - Use _MASK & _SHIFT macro (James)
Changes since V2:
 - use kernel type u8 instead of uint8_t
Changes since V3:
 - Rebase

Signed-off-by: Mahesh Kumar <mahesh1.kumar@intel.com>
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180426142517.16643-4-mahesh1.kumar@intel.com