linker: add an initialized DATA_SECTIONS linker location option

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>

soc/riscv/openisa_rv32m1/linker.ld

@@ -183,6 +183,11 @@ SECTIONS
 #include <linker/common-ram.ld>
 #include <linker/cplusplus-ram.ld>
 
+/* Located in generated directory. This file is populated by the
+ * zephyr_linker_sources() Cmake function.
+ */
+#include <snippets-data-sections.ld>
+
     __data_ram_end = .;
     __data_rom_start = LOADADDR(_DATA_SECTION_NAME);