MFC r330005-r330007, r330021, r330029, r330622, r331207: Solo loader.conf(5)

r330005:
Go back to one loader.conf

We really only need one loader.conf. The other loader.conf was created
because the current one took forever to parse in FORTH. That will be
fixed in the next commit.

r330006:
Take a meat cleaver to defaults/loader.conf

Remove almost all of the _load=XXX options (kept only those relevant
to splash screens, since there were other settings).
Remove the excessively cutesy comment blocks.
Remove excessive comments and replace with similar content
Remove gratuitous blank lines (while leaving some)

We have too many modules to list them all here. There's no purpose in
doing so and it's a giant hassle to maintain. In addition the extra
~500 lines slow this down on small platforms. It slowed it down
so much small platforms forked, which caused other issues...
This is a compromise between those two extremes.

r330007:
loader.conf is loader agnostic, so remove 4th references.

r330021:
These two directories build man pages, so it's incorrect to tag them
NO_OBJ. Also, make sure the loader.conf.5 man gets built and installed.

r330029:
Fix a typo: "now" -> "no".

r330622:
loader.conf(5): Document some other settings

These tend to have less coverage in other places and they don't have
defaults as of yet, so mention them here:
- fdt_overlays
- kernels_autodetect (lualoader only)

r331207:
loader.conf: remove obsolete non-x86 beastie menu statement

As of r330005 the same loader.conf defaults are used on all platforms.