drm/i915/gvt: #include drm_edid.h for drm_edid_block_valid()

As the excessive #includes from i915_drv.h were axed, kvmgt.c build
started failing. Add the necessary #include where needed.

Reported-by: Stephen Rothwell <sfr@canb.auug.org.au>
Fixes: 14da21cc

 ("drm/i915: axe lots of unnecessary includes from i915_drv.h")
Cc: Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com>
Cc: Zhenyu Wang <zhenyuw@linux.intel.com>
Cc: Zhi Wang <zhi.a.wang@intel.com>
Cc: intel-gvt-dev@lists.freedesktop.org
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Reviewed-by: Zhi Wang <zhi.a.wang@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220215122030.2741656-1-jani.nikula@intel.com