Current location options for linker source files includes init and
noinit ram data, but only a noinit ram section. This makes it impossible
for application code to define an initialized RAM output section,
such as with the Z_ITERABLE_SECTION_RAM() helpers.
Adding a DATA_SECTIONS linker source option for this use case.
Signed-off-by: Fabio Baltieri <fabiobaltieri@google.com>