* include/grub/vga.h (grub_vga_write_arx): inb monochrome address as
	well.
	(grub_vga_read_arx): New function.
	* grub-core/video/sis315pro.c (GRUB_SIS315PRO_MMIO_SPACE): New
	definition.
	(framebuffer): New members io, mmioptr and mmiobase.
	(read_sis_cmd): New function.
	(write_sis_cmd): Likewise.
	(grub_video_sis315pro_setup): Do the initialisation. Use 640x480
	rather than 640x400.
	* grub-core/video/sis315_init.c: New file.