This commit renames the symbol CPU_HAS_SYSTICK to
CPU_CORTEX_M_HAS_SYSTICK, to look similar to all
other CPU_CORTEX_M_HAS_ options, and moves the
K-config symbol definition from arm/core/Kconfig to
arm/core/cortex_m/Kconfig.
Signed-off-by: Ioannis Glaropoulos <Ioannis.Glaropoulos@nordicsemi.no>