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

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

Remove the hardcoded IXP425_UART?_VBASE values in the
uart_ixp425_probe() and uart_cpu_getdev(). Change
uart_cpu_getdev() to use hints to find the console.

Reviewed by: marcel

Don't expose the uart_ops structure directly, but instead have
it obtained through the uart_class structure. This allows us
to declare the uart_class structure as weak and as such allows
us to reference it even when it's not compiled-in.
It also allows is to get the uart_ops structure by name, which
makes it possible to implement the dt tag handling in uart_getenv().
The side-effect of all this is that we're using the uart_class
structure more consistently which means that we now also have
access to the size of the bus space block needed by the hardware
when we map the bus space, eliminating any hardcoding.

Gateworks Avila board support:
o ixp425 support
o NPE network driver (requires Intel microcode)
o h/w qmgr support
o True IDE compact flash over expansion bus
o pci (ath and hifn795x parts tested)
o xscale watchdog timer
o ds1672 RTC on i2c bus
o ad7418 voltage + temp monitoring on i2c bus
o uart

Work done together with cognet, kevlo, and jmg. Parts of
the ixp425 support obtaine/derived from netbsd.

Reviewed by: cognet, imp
MFC after: 1 month