Harmony can be booted using device tree with equal functionality as when
booted using a board file. Remove as much of the board file as is
possible, since it's no longer needed.

Two special-cases are still left in board-dt-tegra20.c, since the Tegra
PCIe driver doesn't support device tree yet, and the Harmony .dts file
doesn't yet describe regulators which are needed for PCIe. This logic is
now enabled unconditionally rather than via CONFIG_MACH_HARMONY. While
this is more code than other boards, it's still unlikely to be much of a
problem, and both regulators and PCIe should be supported via device tree
in the near future, allowing the remaining code to be removed.
Signed-off-by: NStephen Warren <swarren@nvidia.com>