ARM: dts: Add 32KHz clock as default clock source

ARM: dts: Add 32KHz clock as default clock source

Clocksource to timer configured in pwm mode can be selected using the DT
property ti,clock-source. There are few pwm timers which are not
selecting the clock source and relying on default value in hardware or
selected by driver. Instead of relying on default value, always select
the clock source from DT.

Signed-off-by: Lokesh Vutla <lokeshvutla@ti.com>
Reviewed-by: Suman Anna <s-anna@ti.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>