Use 115200 bps by default for serial communication

9600 was a standard baud rate decades ago, but 115200 is now more common
so choose defaults that are useful to the largest number of users.

Note that boot0sio does not support rates above 9600 so it remains
unchanged.

Reviewed by: bz, imp, manu
Relnotes: Yes
Sponsored by: The FreeBSD Foundation
Differential Revision: https://reviews.freebsd.org/D36295

Remove $FreeBSD$: one-line sh pattern

Remove /^\s*#[#!]?\s*\$FreeBSD\$.*$\n/

Move the rc framework out of sbin/init into libexec/rc.

The reasons for this are forward looking to pkgbase:
* /sbin/init is a special binary; try not to replace it with
every package update because an rc script was touched.
(a follow-up commit will make init its own package)
* having rc in its own place will allow more easy replacement
of the rc framework with alternatives, such as openrc.

Discussed with: brd (during BSDCam), kmoore
Requested by: cem, bz
PR: 231522
Approved by: re (gjb)