- Copy stable/10@296371 to releng/10.3 in preparation for 10.3-RC1
builds.
- Update newvers.sh to reflect RC1.
- Update __FreeBSD_version to reflect 10.3.
- Update default pkg(8) configuration to use the quarterly branch.

Approved by: re (implicit)

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

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

Use the UART frequency when programming the UART clock.

This allows the 16550 support to work correctly on the upcoming
AR934x support.

For the AR933x UART, the serial clock is not the AHB clock, it's the
reference clock. So use that instead.

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.