Add support for DRI and RSTn markers in JPEG files.

	Add support for DRI and RSTn markers in JPEG files.

	* grub-core/video/readers/jpeg.c (JPEG_MARKER_DRI): New define.
	(JPEG_MARKER_RST0): Likewise.
	(JPEG_MARKER_RST1): Likewise.
	(JPEG_MARKER_RST2): Likewise.
	(JPEG_MARKER_RST3): Likewise.
	(JPEG_MARKER_RST4): Likewise.
	(JPEG_MARKER_RST5): Likewise.
	(JPEG_MARKER_RST6): Likewise.
	(JPEG_MARKER_RST7): Likewise.
	(grub_jpeg_data): New fields dri, r1, bitmap_ptr.
	(grub_jpeg_decode_dri): New function.
	(grub_jpeg_decode_sos): Move image data related part into
	grub_jpeg_decode_data function.
	(grub_jpeg_decode_data): New function.
	(grub_jpeg_reset): New function.
	(grub_jpeg_decode_jpeg): Handle new markers.