drm/i915: Initialize num_scalers for skl and glk too

After commit 1c74eeaf ("drm/i915: Move number of scalers initialization to
runtime init"), scalers are not initialized properly for skl and glk
since num_scalers is left as 0 for those platforms.

Fixes: 1c74eeaf ("drm/i915: Move number of scalers initialization to runtime init")
Cc: Nabendu Maiti <nabendu.bikash.maiti@intel.com>
Cc: Chris Wilson <chris@chris-wilson.co.uk> (v2)
Cc: Ander Conselvan de Oliveira <conselvan2@gmail.com>
Cc: Ander Conselvan de Oliveira <ander.conselvan.de.oliveira@intel.com>
Cc: Daniel Vetter <daniel.vetter@intel.com>
Cc: Jani Nikula <jani.nikula@linux.intel.com>
Cc: intel-gfx@lists.freedesktop.org
Signed-off-by: Ander Conselvan de Oliveira <ander.conselvan.de.oliveira@intel.com>
Tested-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1483365281-10569-1-git-send-email-ander.conselvan.de.oliveira@intel.com