Copy head@r302406 to stable/11 as part of the 11.0-RELEASE cycle.
Prune svn:mergeinfo from the new branch, as nothing has been merged
here.

Additional commits post-branch will follow.

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

Force framebuffer virtual viewport to be the same as physical

VideoCore reports garbage in viewport geometry fields unless
viewport was set previously by earlier stage boot loader. So
when booting FreeBSD kernel directly from VideoCore's start.elf
framebuffer intialization fails due to invalid vxres, vyres
values. Make sure we request viewport to be equal to physical
resolution

Submitted by: Sylvain Garrigues <sylvain@sylvaingarrigues.com>

Refactor mailbox property API to make it usable for /dev/vcio driver:

- Add bcm2835_mbox_property for generic property request, it accepts
pointer to prepared property chan message and its size, forwards
it to MBOX and copies result back
- Make all bcm2835_mbox_XXX functions that use property channel go
through bcm2835_mbox_property path. Do not accept device_t as
an argument, it's not required: all DMA operatiosn should go
through mbox device, and all API consumers should report errors
on their side.

Add mailbox tag/structure for touchscreen buffer address property

Add the routines to query and setup the framebuffer state using the
BCM2835_MBOX_CHAN_PROP channel. The old channel (BCM2835_MBOX_CHAN_FB)
seems deprecated on recent firmware versions and is causing a freeze on
RPi 2.

The actual changes in the framebuffer drivers will follow in subsequent
commits.

Add a helper function to read clock frequencies from videocore and use this
to get the default frequency of the sdhci device.

While here use a u_int to hold the frequency as it may be too large to fit
in a 32-bit signed integer. This is the case when we have a 250MHz clock.

Move the code to set the device power to the bcm2835 mailbox driver so it
can be reused by other drivers.

Add the structures needed to get/set the power state. These can be used
when, for example, we boot without U-Boot and wish to enable USB, or to
suspend an unneeded device.

MFC after: 1 week

Driver for CPU frequency/voltage control on the Raspberry Pi.

Differential Revision: https://reviews.freebsd.org/D1025
Submitted by: Daisuke Aoyama aoyama@peach.ne.jp
Reviewed by: ian (earlier version), rpaulo
MFC after: 1 month
Relnotes: yes