config-list.mk: Add arc configurations.
        * config/arc/arc.h (HARD_REGNO_NREGS): Use ARC_FIRST_SIMD_VR_REG /
        ARC_LAST_SIMD_VR_REG.
        * config/arc/arc.c (arc_conditional_register_usage): Likewise.
        Also set reg_alloc_order for DMA config regs.