drm/loongson/7a1000: convert to struct drm_edid

Prefer the struct drm_edid based functions for reading the EDID and
updating the connector.

Reviewed-by: Sui Jingfeng <sui.jingfeng@linux.dev>
Link: https://patchwork.freedesktop.org/patch/msgid/22c66af62cd5ae1998bbaf6801cda3cc689f9e3f.1715691257.git.jani.nikula@intel.com


Signed-off-by: Jani Nikula <jani.nikula@intel.com>