drm/i915: Add has_psr-flag to gen9lp

While testing Jim Bride's latest batch of PSR patches I noticed
that gen9lp doesn't include the has_psr flag, and that our GLK
system thus reported PSR as unsupported.

This patch simply adds has_psr.

Signed-off-by: David Weinehall <david.weinehall@linux.intel.com>
Acked-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Reviewed-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20170808100952.26448-1-david.weinehall@linux.intel.com