soc: intel_adsp: fix linker script for cavs_v20

Apply a similar fix for cavs_v20 as was done for other cavs platforms in
commit ee7773fb ("soc: intel_adsp: fix linker script for XCC").
Without this fix, cavs_v20 build with fail with 0.13.0 Zephyr SDK.

Fixes: 74cc8bee ("xtensa: cavs_v20: use uncached addresses to support SMP")
BugLink: https://github.com/thesofproject/sof/issues/4703


Signed-off-by: Kai Vehmanen <kai.vehmanen@linux.intel.com>