Add KPnS (known problems and solutions) entries:

• /dev/ttyv* not found on FreeBSD/sparc64 when there is no framebuffer[1].
• KLDs do not work on FreeBSD/sparc64 with >4GB RAM[2].
• kgdb is broken for debugging panics on FreeBSD/sparc64[2].

Thanks to: marius[1], kris[2]
Approved by: re (implicitly)