xHCI: Adding #define values used for hub descriptor

xhci-hub used some numerical values for initialisation of root hub
descriptors. #define values are addded in usb 2.0 hub specification
file and these values are used for root hub characteristics
initialisation.

Also use some #defines in places where magic numbers are being used.

Signed-off-by: Aman Deep <amandeep3986@gmail.com>
Acked-by: Sarah Sharp <sarah.a.sharp@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>