HDR metadata block is introduced in CEA-861.3 spec.
Parsing the same to get the panel's HDR metadata.

v2: Rebase and added Ville's POC changes to the patch.

v3: No Change

v4: Addressed Shashank's review comments

v5: Addressed Shashank's comment and added his RB.

v6: Addressed Jonas Karlman review comments.

v7: Adressed Ville's review comments and fixed the issue
with length handling.

v8: Put the length check as per the convention followed in
existing code, as suggested by Ville.
Signed-off-by: NUma Shankar <uma.shankar@intel.com>
Reviewed-by: NShashank Sharma <shashank.sharma@intel.com>
Signed-off-by: NVille Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/1558015817-12025-4-git-send-email-uma.shankar@intel.com