drm/edid: add drm_edid helper for drm_detect_hdmi_monitor()

We'll need to propagate drm_edid everywhere.

v2: Handle NULL EDID pointer (Ville, CI)

Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Reviewed-by: Ankit Nautiyal <ankit.k.nautiyal@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/2fbee0d7b544b44ef0866bb154beefac5d260bec.1652097712.git.jani.nikula@intel.com