A broken implementation of is_pot() prevented the detection of when a
singular pipe was enabled. Eric Anholt pointed out the existence of
is_power_of_2() so use that instead of our broken code!

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=35402Signed-off-by: NYuanhan Liu <yuanhan.liu@intel.com>
Tested-by: xunx.fang@intel.com
Reviewed-by: NKeith Packard <keithp@keithp.com>
Signed-off-by: NChris Wilson <chris@chris-wilson.co.uk>