ARM: Tegra186: calculate load addresses at boot

In the presence of potentially fragemented memory, we cannot hard-code
addresses into environment variables such as kernel_addr_r. Instead, we
must calculate those addresses at run-time based on available memory
locations. Implement the code to perform such runtime calculation, based
on requirements described in environment variables, to allow the user
full control over the allocation.

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