Add ARC as an arch that supports PCI_MSI_IRQ_DOMAIN and add generation of
msi.h in the ARC arch.

Signed-off-by: Joao Pinto <jpinto@synopsys.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Acked-by: Vineet Gupta <vgupta@synopsys.com>