zephyr: link the .unstable_id data in ROM

The data in this section is constant:

const char _chreVersionString[]...

So it can be linked in ROM, which also solves a build issue with few
platforms upstream as this linker section is not supposed to use RAM
data in the first place.

Signed-off-by: Fabio Baltieri <fabiobaltieri@google.com>

platform/zephyr/linker_chre.ld

@@ -17,5 +17,4 @@
 SECTION_DATA_PROLOGUE(_CHRE_SECTION,,)
 {
 	KEEP(*(".unstable_id"));
-} GROUP_DATA_LINK_IN(RAMABLE_REGION, ROMABLE_REGION)
-
+} GROUP_ROM_LINK_IN(RAMABLE_REGION, ROMABLE_REGION)