Cleanup PCI_ENDPOINT_TEST memspace (by moving the interrupt number away
from command section).

Add IRQ_TYPE register to identify the triggered ID interrupt required
for the READ/WRITE/COPY tests and raise IRQ test commands.

Update documentation accordingly.
Signed-off-by: NGustavo Pimentel <gustavo.pimentel@synopsys.com>
Signed-off-by: NLorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Acked-by: NKishon Vijay Abraham I <kishon@ti.com>