arm64: tegra: Fixup SYSRAM references

The json-schema bindings for SRAM expect the nodes to be called "sram"
rather than "sysram" or "shmem". Furthermore, place the brackets around
the SYSRAM references such that a two-element array is created rather
than a two-element array nested in a single-element array. This is not
relevant for device tree itself, but allows the nodes to be properly
validated against json-schema bindings.

Signed-off-by: Thierry Reding <treding@nvidia.com>