We cannot enter sleep_while_idle if some functional clocks are
active. Add a check for enabled functional clocks for 34xx.

Note that this workaround could be behind CONFIG_PM_DEBUG
option when all drivers are configuring their sysconfig
registers properly and using their clocks properly.
Signed-off-by: Jouni Hogander <jouni.hogander@nokia.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>