ARM: tegra: fix malloc region sizing

ARM: tegra: fix malloc region sizing

Commit 52a7c98a1772 "tegra-common: increase malloc pool len by dfu mmc
file buffer size" updated the definition of CONFIG_SYS_MALLOC_LEN for
Tegra to take account of the DFU buffer size. However, this change had
no effect, since typical Tegra board config headers don't set the DFU-
related defines until after tegra-common.h is included. Fix this by
moving the affected conditional code to tegra-common-post.h, which is
included last. Also move the definition of SYS_NONCACHED_MEMORY since
it's a related and adjacent definition.

Fix the condition to test for the DFU feature, rather than specifically
MMC DFU support, so it applies in all cases.

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