i915: do not setup intel_backlight twice

The commit "Not all systems expose a firmware or platform mechanism for
changing the backlight intensity on i915, so add native driver support"
adds calls to  intel_panel_setup_backlight() from intel_{lvds,dp}_init
so do not call it again from intel_setup_outputs().

BugLink: http://bugs.launchpad.net/bugs/831542



Signed-off-by: Kamal Mostafa <kamal@canonical.com>
ACKed-by: Matthew Garrett <mjg@redhat.com>
Signed-off-by: Keith Packard <keithp@keithp.com>