ARM: tegra: trimslice: initialize PCI-e only when running on TrimSlice

Currently tegra_pcie_init is effectively called as subsys_initcall. With
multiplatform kernel this may cause hangs on boards that don't intend to
support Tegra2 PCI-e. Ensure that TrimSlice board code initializes PCI-e
only when actually running on the TrimSlice.

Signed-off-by: Mike Rapoport <mike@compulab.co.il>
Signed-off-by: Colin Cross <ccross@android.com>