arm64: tegra: Add configuration for PCIe C5 sideband signals

Add support to configure PCIe C5's sideband signals PERST# and CLKREQ#
as output and bi-directional signals respectively which unlike other
PCIe controllers sideband signals are not configured by default.

Signed-off-by: Vidya Sagar <vidyas@nvidia.com>
Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Reviewed-by: Andrew Murray <andrew.murray@arm.com>