Fix test_pc009.c Async mode

Skip asynchronous CAP_SET test for powercap domains NOT supporting
asynchronous cap setting and make sure that no delayed response is
set when an asynchronus CAP_SET with the Ignore flag is requested.
Al fix the test to check tagainst powercap protocol instead of clock.

Signed-off-by: Cristian Marussi <cristian.marussi@arm.com>