usb_power_delivery: Handle extended message type in PD 3.0

usb_power_delivery: Handle extended message type in PD 3.0

The Message Type field of USB PD 3.0 messages has been extended from 4
to 5 bits[1]. While the protocol decoder already knows about the newly
defined message types (such as Get_Source_Cap_Extended), it does not
handle them correctly, because only the lower 4 bits of the header are
masked off (resulting, for example, in GoodCRC being detected, instead
of Get_Source_Cap_Extended).

Fix this by increasing the size of the Message Type field depending on
the value of the Specification Revision field.

[1] See Tables 6-1 of the USB Power Delivery Specification Revision 2.0
and Revision 3.0, respectively.