drm/armada: Use devm_drm_dev_alloc

drm/armada: Use devm_drm_dev_alloc

Also remove the now no longer needed build bug on since that's already
not needed anymore with drmm_add_final_kfree. Conversion to managed
drm_device cleanup is easy, the final drm_dev_put() is already the
last thing in both the bind unbind as in the unbind flow.

Also, this relies on component.c correctly wrapping bind&unbind in
separate devres groups, which it does.

Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
Reviewed-by: Dave Airlie <airlied@redhat.com>
Cc: Russell King <linux@armlinux.org.uk>
Link: https://patchwork.freedesktop.org/patch/msgid/20200904143941.110665-2-daniel.vetter@ffwll.ch