Copy head (r256279) to stable/10 as part of the 10.0-RELEASE cycle.

Approved by: re (implicit)
Sponsored by: The FreeBSD Foundation

Fix the scc(4) module build. Without the file it's missing a required symbol.

Approved by: nwhitehorn (mentor)
MFC after: 3 days

MFtbemd: use MACHINE_CPUARCH

Don't build unused SBus front-ends for sun4v, don't build EBus front-ends
which are also likely to be irrelevant for sun4v (there's no SBus on sun4v
and only some EBus devices). While at it fix some style bugs according to
style.Makefile(5) where appropriate.

MFC after: 3 days

Include the QUICC bus front-end in the module for PowerPC.

Build the scc(4) module with EBus and SBus attachments for sparc64
only and build the scc(4) module with MacIO attachment for powerpc.

Add scc(4), a driver for serial communications controllers. These
controllers typically have multiple channels and support a number
of serial communications protocols. The scc(4) driver is itself
an umbrella driver that delegates the control over each channel
and mode to a subordinate driver (like uart(4)).
The scc(4) driver supports the Siemens SAB 82532 and the Zilog
Z8530 and replaces puc(4) for these devices.