PCI: tegra: Read "dbi" base address to program in application logic

PCIe controller in Tegra194 requires the "dbi" region base address to be
programmed in one of the application logic registers to enable CPU access
to the "dbi" region. But, commit a0fd361d ("PCI: dwc: Move "dbi",
"dbi2", and "addr_space" resource setup into common code") moved the code
that reads the whereabouts of "dbi" region to the common code causing the
existing code in pcie-tegra194.c file to program NULL in the application
logic registers. This is causing null pointer dereference when the "dbi"
registers are accessed. This issue is fixed by explicitly reading the
"dbi" base address from DT node.

Link: https://lore.kernel.org/r/20201125192554.5401-1-vidyas@nvidia.com
Fixes: a0fd361d

 ("PCI: dwc: Move "dbi", "dbi2", and "addr_space" resource setup into common code")
Tested-by: Thierry Reding <treding@nvidia.com>
Signed-off-by: Vidya Sagar <vidyas@nvidia.com>
Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Acked-by: Thierry Reding <treding@nvidia.com>