clocksource/drivers/timer-ti-dm: Save and restore timer TIOCP_CFG

As we are using cpu_pm to save and restore context, we must also save and
restore the timer sysconfig register TIOCP_CFG. This is needed because
we are not calling PM runtime functions at all with cpu_pm.

Fixes: b34677b0

 ("clocksource/drivers/timer-ti-dm: Implement cpu_pm notifier for context save and restore")
Cc: Aaro Koskinen <aaro.koskinen@iki.fi>
Cc: Adam Ford <aford173@gmail.com>
Cc: Andreas Kemnade <andreas@kemnade.info>
Cc: Lokesh Vutla <lokeshvutla@ti.com>
Cc: Peter Ujfalusi <peter.ujfalusi@gmail.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>
Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>
Link: https://lore.kernel.org/r/20210415085506.56828-1-tony@atomide.com