Fix EHCI low-speed.

	Fix EHCI low-speed.

	* grub-core/bus/usb/ehci.c (GRUB_EHCI_MULT_ONE): Fix the value.
	(GRUB_EHCI_MULT_TWO): Likewise.
	(GRUB_EHCI_MULT_THREE): Likewise.
	(GRUB_EHCI_CMASK_MASK): New enum value.
	(GRUB_EHCI_SMASK_MASK): Likewise.
	(GRUB_EHCI_CMASK_OFF): Likewise.
	(GRUB_EHCI_SMASK_OFF): Likewise.
	(grub_ehci_pci_iter): Enable periodic schedule.
	(grub_ehci_parse_notrun): Likewise.
	(grub_ehci_restore_hw): Likewise.
	(grub_ehci_setup_qh): Set flags for low speed transfers.
	(grub_ehci_find_qh): Use periodic list for low speed.
	(grub_ehci_setup_transfer): Check periodic queue as well.
	(grub_ehci_check_transfer): Likewise.
	(grub_ehci_cancel_transfer): Cancel periodic transfer.