ARM: tegra: use CONFIG_SYS_INIT_SP_BSS_OFFSET

Enable CONFIG_SYS_INIT_SP_BSS_OFFSET for all 64-bit Tegra boards. Place
the stack/... 512KiB from the end of the U-Boot binary. This should be
plenty to accommodate the current DTBs (max 64 KiB), early malloc region
(6KiB), stack usage, and plenty of slack, while still not placing it too
far away from the U-Boot binary.

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