ARM: tegra: remove dead code

Now that all boards are converted to device tree, devices.[ch] and
board-pinmux.[ch] are no longer used. So, remove them.

The only exception is the EHCI platform data in devices.h. Move that
data to board-dt-tegra20.c - the only places it's used.

Signed-off-by: Stephen Warren <swarren@nvidia.com>