iatu_unroll_enabled flag is set only for Designware in host mode.

However iATU unroll can be applicable for endpoint mode too. Set
iatu_unroll_enabled flag in dw_pcie_setup() which is common for
both host mode and endpoint mode.
Signed-off-by: Kishon Vijay Abraham I <kishon@ti.com>
Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>