OMAP4: DPLL cascading: exit cascading before system restart

Exiting from DPLL cascading on system restart should be done before CPUs are turned off.
In other case deadlocks are possible when mutex locked with idled CPU could be acquired
with an active CPU.

Change-Id: I608f8aee6c6f3e9a2c1fca0f06ea836222b121c2
Signed-off-by: Taras Kondratiuk <taras@ti.com>
Signed-off-by: Andrii Tseglytskyi <andrii.tseglytskyi@ti.com>
Signed-off-by: Volodymyr Mieshkov <volodymyr.mieshkov@ti.com>