arm64: gic: its-trigger: Don't trigger the LPI while it is pending

The its-trigger test checks that LPI 8195 is not delivered to the CPU while
it is disabled at the ITS level. After that it is re-enabled and the test
checks that the interrupt is properly asserted. After it's re-enabled and
before the stats are examined, the test triggers the interrupt again, which
can lead to the same interrupt being delivered twice: once after the
configuration invalidation and before the INT command, and once after the
INT command.

Get rid of the INT command after the interrupt is re-enabled to prevent the
LPI from being asserted twice and add a separate check to test that the INT
command still works for the now re-enabled LPI 8195.

CC: Auger Eric <eric.auger@redhat.com>
Suggested-by: Zenghui Yu <yuzenghui@huawei.com>