Need to have a "SRAM retention" section for code

Need to have linker sections for low power operation, and a function that restores when a system comes out of low power state, along with retained RAM areas, that can do operation and checking, when in super low power states.

The issue does not name any files, tests, or entry points. Start by locating the linker configuration and low-power management code, then determine how retained RAM is represented and restored. Done means the requested linker sections, wake-from-low-power restoration function, and retained-RAM operation and checking are defined and covered by relevant tests.

Written by the indexing model from the issue text.