modules: CMSIS_6: Switch to CMSIS_6 for Cortex-M

What is the change?
Switch to module CMSIS_6 for Cortex-M while continuing to use
cmsis module (version 5.9.0) for Cortex-A/R.

Why do we need this change?

The current cmsis module consists of:
- Cortex-M support from upstream cmsis 5.9.0
- Cortex-A/R support which was not upstreamed to CMSIS

Upstream cmsis 5.9 was deprecated so we should be using CMSIS_6 however,
it seems due to lack of Cortex-A/R support in upstream and other reasons,
this was pushed back.

While upstreaming Cortex-A/R support to CMSIS_6 could take its time,
this shouldn't stop Cortex-M to start using CMSIS_6.

Also, if we do not use CMSIS_6 for Cortex-M then using the
newer GCC 14.2 toolchain will return below compiler error:
```
zephyrproject/modules/hal/cmsis/CMSIS/Core/Include/core_cm85.h:4406:10:
fatal error: pac_armv81.h: No such file or directory
 4406 | #include "pac_armv81.h"
```
Using CMSIS_6 for Cortex-M will fix this.

Signed-off-by: Sudan Landge <sudan.landge@arm.com>