Add 9.3 to mdoc.local.

Sponsored by:	The FreeBSD Foundation
Spell always the more traditional way.
We have to include bsd.opts.mk (included in bsd.own.mk) after
/etc/src.conf so that options set there will affect the options
defined in bsd.opts.mk. Fix a few comments while I'm here.
Add the codes for enabling CPU cores of Rockchip RK3188 SoC.
Enable SMP for Radxa Rock board.

Approved by:	stas (mentor)