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>