ARM: tegra: Use mem size from MC in combination with get_ram_size()

On popular request this now completes the Warren's work started for
TK1:

aeb3fcb3
ARM: tegra: Use mem size from MC rather than ODMDATA

In addition to the move of using the Tegra memory controller (MC)
register rather than ODMDATA for T20, T30 and T114 as well it further
uses the generic get_ram_size() function (see "common/memsize.c")
<supposed to be used in each and every U-Boot port>TM. Added benefit is
that it should <catch 99% of hardware related (i. e. reliably
reproducible) memory errors> as well.

Thoroughly tested on the various Toradex line of Tegra modules
available which unfortunately does not include T114 and T124 (yet at
least) plus on the Jetson TK1.

Based-on-work-by: Stephen Warren <swarren@nvidia.com>
Based-on-work-by: Tom Warren <twarren@nvidia.com>
Signed-off-by: Marcel Ziswiler <marcel@ziswiler.com>
Acked-by: Stephen Warren <swarren@nvidia.com>
Signed-off-by: Tom Warren <twarren@nvidia.com>