pci: tegra: fix DM conversion issues on Tegra20

pci: tegra: fix DM conversion issues on Tegra20

Tegra20's PCIe controller has a couple of quirks. There are workarounds in
the driver for these, but they don't work after the DM conversion:

1) The PCI_CLASS value is wrong in HW.

This is worked around in pci_tegra_read_config() by patching up the value
read from that register. Pre-DM, the PCIe core always read this via a
16-bit access to the 16-bit offset 0xa. With DM, 32-bit accesses are used,
so we need to check for offset 0x8 instead. Mask the offset value back to
32-bit alignment to make this work in all cases.

2) Accessing devices other than dev 1 causes a data abort.

Pre-DM, this was worked around in pci_skip_dev(), which the PCIe core code
called during enumeration while iterating over a bus. The DM PCIe core
doesn't use this function. Instead, enhance tegra_pcie_conf_address() to
validate the bdf being accessed, and refuse to access invalid devices.
Since pci_skip_dev() isn't used, delete it.

I've also validated that both these WARs are only needed for Tegra20, by
testing on Tegra30/Cardhu and Tegra124/Jetson TKx. So, compile them in
conditionally.

Fixes: e81ca88451cf ("dm: tegra: pci: Convert tegra boards to driver model for PCI")
Signed-off-by: Stephen Warren <swarren@nvidia.com>
Reviewed-by: Thierry Reding <treding@nvidia.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
Signed-off-by: Tom Warren <twarren@nvidia.com>