ARM: tegra: use standard variables to define load addresses

ARM: tegra: use standard variables to define load addresses

Currently, Tegra's default environment uses non-standard variables to define
where boot scripts should load the kernel, FDT, and initrd. This change both
changes the variable names to match those described in U-Boot's README, and
shuffles their values around a little so that the values make a little more
sense; see comments in the patch for rationale behind the values chosen.

Note that this patch does remove the old non-standard variable "fdt_load" from
the default environment, so this patch requires people to change their boot
scripts.

Signed-off-by: Stephen Warren <swarren@nvidia.com>
Acked-by: Simon Glass <sjg@chromium.org>
Signed-off-by: Tom Warren <twarren@nvidia.com>