soc: xtensa: fix missing rodata section in intel_adsp

The common linker script for cavs_v?? was missing an include for the
snippets-rodata.ld file which is needed for any applications using the
`zephyr_linker_source(RODATA <linker_script>)` cmake function.

Signed-off-by: Yuval Peress <peress@google.com>