PCI: tegra: Fix afi_pex2_ctrl reg offset for Tegra30

Fix AFI_PEX2_CTRL reg offset for Tegra30 by moving it from the Tegra20
SoC struct where it erroneously got added. This fixes the AFI_PEX2_CTRL
reg offset being uninitialised subsequently failing to bring up the
third PCIe port.

Fixes: adb2653b ("PCI: tegra: Add AFI_PEX2_CTRL reg offset as part of SoC struct")
Signed-off-by: Marcel Ziswiler <marcel@ziswiler.com>
Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Reviewed-by: Andrew Murray <andrew.murray@arm.com>
Acked-by: Thierry Reding <treding@nvidia.com>