drm/radeon/kms: minor fixes for eDP with LCD* device tags (v2)

Some systems have LCD* rather than DFP* device tags in the bios
for eDP connectors; notably the new apple iMac. This fixes
things up so eDP connectors with either tag will work.

v2: fix typo

Signed-off-by: Alex Deucher <alexdeucher@gmail.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>