ure.4: add a HARDWARE section + add RTL8156BG as a compatible controller

While here, rename all instances of "RealTek" to "Realtek" for
authenticity.

Approved by: re (cperciva)
Reviewed by: imp, lwshu, zaiee
Pull Request: https://github.com/freebsd/freebsd-src/pull/1649

(cherry picked from commit 76ed6f2db316bf2240d36d3c92316da4d1e5b174)
(cherry picked from commit f336a04960b608d2caeaf964663c3a8425f31d71)