arm/dt: tegra: Remove /chosen node

The command-lines present in the existing /chosen node are not necessarily
correct for all users. Ideally, we should simply use the command-line
supplied by the boot-loader.

In fact, using the boot-loader's cmdline is quite easy; either the
bootloader fully supports DT, in which case it can modify the DT passed
to the kernel to include its command-line, or CONFIG_APPENDED_DTB can
be used in conjunction with CONFIG_ARM_ATAG_DTB_COMPAT, and the kernel
will substitute the bootloader's command-line into the DT.

Signed-off-by: Stephen Warren <swarren@nvidia.com>
Signed-off-by: Olof Johansson <olof@lixom.net>