Refactor z_arch_is_user_context() for ARM, so it uses the CMSIS CONTROL_nPRIV_Msk instead of hard-coded 0x1. Fixing also some typos in include/arch/arm/syscall.h. Signed-off-by: Ioannis Glaropoulos <Ioannis.Glaropoulos@nordicsemi.no>