PCI: designware: Fix iATU programming for cfg1, io and mem viewport

This patch corrects iATU programming for cfg1, io and mem viewport.  Enable
ATU only after configuring it.

Signed-off-by: Mohit Kumar <mohit.kumar@st.com>
Signed-off-by: Ajay Khandelwal <ajay.khandelwal@st.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Acked-by: Jingoo Han <jg1.han@samsung.com>
Cc: stable@vger.kernel.org