arm64: dts: ti: k3-am64-main: Add ecap pwm nodes

There are 3 instances of ecap modules that are capable of generating
a pwm when configured in apwm mode. Add DT nodes for these 3 ecap
instances.

Signed-off-by: Lokesh Vutla <lokeshvutla@ti.com>
Signed-off-by: Nishanth Menon <nm@ti.com>
Reviewed-by: Grygorii Strashko <grygorii.strashko@ti.com>
Link: https://lore.kernel.org/r/20210721113625.17299-3-lokeshvutla@ti.com