drm/edid: check for HF-VSDB block

This patch implements a small function that finds if a
given CEA db is hdmi-forum vendor specific data block
or not.

V2: Rebase.
V3: Added R-B from Jose.
V4: Rebase
V5: Rebase
V6: Rebase
V7: Rebase
V8: Rebase
V9: Rebase
V10: Rebase

Signed-off-by: Thierry Reding <treding@nvidia.com>
Signed-off-by: Shashank Sharma <shashank.sharma@intel.com>
Reviewed-by: Jose Abreu <joabreu@synopsys.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1489404244-16608-3-git-send-email-shashank.sharma@intel.com