west.yml: Import cmsis_6 to be used by SOF for Cortex-M targets

After commit
f726cb5123eda12fe ("modules: CMSIS_6: Switch to CMSIS_6 for Cortex-M")
SOF needs cmsis_6 to be used for Cortex-M (imx95).

So import cmsis_6 and fix the compilation error.

Fixes: #10014
Signed-off-by: Daniel Baluta <daniel.baluta@nxp.com>

Author: dbaluta

west.yml

@@ -60,6 +60,7 @@ manifest:
           - lz4
           - tinycrypt
           - cmsis
+          - cmsis_6
 
   self:
     # Changes to submanifests/*.yml files _are_ effective; these have no