ARM: Tegra: Make tegra_dma_init a postcore_initcall

The following commit makes the Tegra APB DMA engine fail to initialize
correctly: 0cf6230a
ARM: tegra: Move tegra_common_init to tegra_init_early

The reason is that tegra_init_early_ calls tegra_dma_init which calls
request_threaded_irq, which fails since the IRQ hasn't yet been marked
valid; that only happens in tegra_init_irq, which gets called after
tegra_init_early.

This used to work OK, since tegra_init_early was tegra_common_init, which
got called after tegra_init_irq, basically from the beginning of
tegra_harmony_init.

Solve this by converting tegra_dma_init to a postcore_initcall. This makes
it execute late enough that IRQs are marked valid, and avoids having to
add it back to every machine's init function.

Signed-off-by: Stephen Warren <swarren@nvidia.com>
Signed-off-by: Colin Cross <ccross@android.com>