tests: arch: arm: arm_runtime_nmi: Add filter for Cortex-M

This commit adds a filter to restrict the `arch/arm/arm_runtime_nmi`
test to the ARM Cortex-M platforms only, since this test currently
does not support the Cortex-A and Cortex-R platforms.

Signed-off-by: Stephanos Ioannidis <root@stephanos.io>