Bitfields for OpenHCI "HcControlHeadED"/"HcControlCurrentED" register:
Bit(s)	Description	)
 31-4	physical address of first/current Endpoint Descriptor (bits 31-4)
 3-0	reserved (0)
Note:	HcControlCurrentED is set to 0000000h to indicate the end of the
	  Control list
SeeAlso: #00902,#00908,#00909