tests: kernel: fatal: add explicit test case for ARM and FP Sharing mode

For the ARM architecture we would like to test the HW
Stack Protection feature when building with support for
FP shared registers mode (CONFIG_FP_SHARING=y), as a
means of increasing coverage.

Signed-off-by: Ioannis Glaropoulos <Ioannis.Glaropoulos@nordicsemi.no>