_vga_gdc_write
_vga_gdc_write(vh, i, regs->gdc[i]);
_vga_gdc_write(vh, i, vga_gdc[i]);
_vga_gdc_write(vh, offsetof(struct reg_vgagdc, reg), val)
static __inline void _vga_gdc_write(struct vga_handle *, int, u_int8_t);