ARM: dts: am33xx: Drop interrupt property from ecap nodes

Interrupts were never supported by ecap driver and the bindings
were never documented.Therefore drop the entries in preparation
to moving bindings to YAML schema.

Signed-off-by: Lokesh Vutla <lokeshvutla@ti.com>
Reviewed-by: Grygorii Strashko <grygorii.strashko@ti.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>