xtensa: cavs_v20: use uncached addresses to support SMP

SMP support on cAVS is implemented by using uncached addresses for all
writable data sections except for stack, i.e. for .data, .bss and
some other specialised ones. So far that has been implemented for
cAVS 1.5/1.8. This patch does the same for cAVS 2.0.

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