Document additions from reviews D34687 and D34764 in cgem.4 manpage

[bsd_dino.sk]

Summary

Review D34687 added if_cgem as loadable module.
Review D34764 added SGMII connection mode and some enhancements.
Document those in relevant manpage,

[pauamma_gundo.com]

I'm not sure I understand the driver changes this is meant to document. Someone else will have to check for consistency with that. Perhaps the reviewer(s) for these changes. Meanwhile, could you upload a full diff next time as already requested in one of these reviews?

share/man/man4/cgem.4

110

s/RGMII,/RGMII;/ (comma splice)

111

s/in device tree/in the device tree/

[pauamma_gundo.com]

English LGTM now but it really needs a subject matter expert to look at it.

[mhorne]

share/man/man4/cgem.4

54

While here, you could tweak this to mention the HiFive Unmatched instead. It is a more relevant example.

111–113

IMO, device tree properties are beyond the scope of what we would expect in a driver man page. I think it is enough to say the following:

The
.Nm
driver supports GMII, RGMII, and SGMII PHY connection modes.