bnxt.4: Adjust for recent HARDWARE

+ Adjust document description matching another terabit driver
+ Add BCM576XX family to DESCRIPTION, switch to XX notation
+ Add some model names, additional models, and improvements to HARDWARE

MFC after: 3 days
Reviewed by: sumit.saxena_broadcom.com (previous)
Differential Revision: https://reviews.freebsd.org/D54028