PCI: tegra194: Fix MCFG quirk build regressions

7f100744 ("PCI: tegra: Add Tegra194 MCFG quirks for ECAM errata")
caused a few build regressions:

  - 7f100744 removed the Makefile rule for CONFIG_PCIE_TEGRA194, so
    pcie-tegra.c can no longer be built as a module.  Restore that rule.

  - 7f100744 added "#ifdef CONFIG_PCIE_TEGRA194" around the native
    driver, but that's only set when the driver is built-in (for a module,
    CONFIG_PCIE_TEGRA194_MODULE is defined).

    The ACPI quirk is completely independent of the rest of the native
    driver, so move the quirk to its own file and remove the #ifdef in the
    native driver.

  - 7f100744 added symbols that are always defined but used only when
    CONFIG_PCIEASPM, which causes warnings when CONFIG_PCIEASPM is not set:

      drivers/pci/controller/dwc/pcie-tegra194.c:259:18: warning: ‘event_cntr_data_offset’ defined but not used [-Wunused-const-variable=]
      drivers/pci/controller/dwc/pcie-tegra194.c:250:18: warning: ‘event_cntr_ctrl_offset’ defined but not used [-Wunused-const-variable=]
      drivers/pci/controller/dwc/pcie-tegra194.c:243:27: warning: ‘pcie_gen_freq’ defined but not used [-Wunused-const-variable=]

Fixes: 7f100744

 ("PCI: tegra: Add Tegra194 MCFG quirks for ECAM errata")
Link: https://lore.kernel.org/r/20210610064134.336781-1-jonathanh@nvidia.com
Signed-off-by: Jon Hunter <jonathanh@nvidia.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Reviewed-by: Thierry Reding <treding@nvidia.com>