cxgbe(4):  Recognize the "spider" configuration where a T5 card's 40G
QSFP port is presented as 4 distinct 10G SFP+ ports to the driver.

MFC after:	2 weeks

Ticket: #4922

(cherry picked from commit 220e798d63f9c03403ac667760f439be007d7e93)
(cherry picked from commit 14af79259c271d27a4d85cecb62bd42553636e09)