PCI: tegra: Remove unused struct tegra_pcie_bus

Following the code refactoring completed in the commit 1fd92928


("PCI: tegra: Refactor configuration space mapping code") there are no
more known users of struct tegra_pcie_bus.

Thus, remove declaration of struct tegra_pcie_bus as it's no longer
needed and does not have any existing users left.

Link: https://lore.kernel.org/r/20210704235733.2514131-1-kw@linux.com
Signed-off-by: Krzysztof Wilczyński <kw@linux.com>
Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>