ARM / shmobile: Return -EBUSY from A4LC power off if A3RV is active

Since the A4LC should only be powered off if the A3RV is off, make
the A4LC's power down routine return -EBUSY if A3RV is not off to
indicate to the core that it doesn't want to power off the domain in
that case.  This will cause the core to regard A4LC as active, so
the pm_genpd_poweron() in pd_power_down_a3rv() is not necessary any
more.

Signed-off-by: Rafael J. Wysocki <rjw@sisk.pl>
Acked-by: Magnus Damm <damm@opensource.se>