drm: Add drm_mode_init()

Add a variant of drm_mode_copy() that explicitly clears out
the list head of the destination mode. Helpful to guarantee
we don't have stack garbage left in there for on-stack modes.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220218100403.7028-2-ville.syrjala@linux.intel.com


Reviewed-by: Andrzej Hajda <andrzej.hajda@intel.com>
Reviewed-by: Harry Wentland <harry.wentland@amd.com>