- Copy stable/10 (r259064) to releng/10.0 as part of the
10.0-RELEASE cycle.
- Update __FreeBSD_version [1]
- Set branch name to -RC1

[1] 10.0-CURRENT __FreeBSD_version value ended at '55', so
start releng/10.0 at '100' so the branch is started with
a value ending in zero.

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

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

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

Bring over the initial, CPU-only UART support for the AR933x SoC.

This implements the kernel glue needed (getc, putc, rxready).

This isn't a 16550 UART, even if the datasheet overview claims so.

The Linux ar933x support was used as a reference, however the uart code
is a reimplementation.

Attentive viewers will note that the uart code is based off of the ns8250
code and the UART bus code is a stubbed-out version of this. I'll be
replacing it with non-stubbed versions soon, making this a fully featured
driver.

Tested:

* AP121 reference board (AR933x), booting through the mountroot> prompt;
then doing some basic interactive tests in ddb.