mailbox: Introduce framework for mailbox

Introduce common framework for client/protocol drivers and
controller drivers of Inter-Processor-Communication (IPC).

Client driver developers should have a look at
 include/linux/mailbox_client.h to understand the part of
the API exposed to client drivers.
Similarly controller driver developers should have a look
at include/linux/mailbox_controller.h

Signed-off-by: Jassi Brar <jaswinder.singh@linaro.org>
Reviewed-by: Mark Brown <broonie@linaro.org>
doc: add documentation for mailbox framework

 Some explanations with examples of how to write to implement users
and providers of the mailbox framework.

Signed-off-by: Jassi Brar <jaswinder.singh@linaro.org>
dt: mailbox: add generic bindings

Define generic bindings for the framework clients to
request mailbox channels.

Signed-off-by: Jassi Brar <jaswinder.singh@linaro.org>
Reviewed-by: Mark Brown <broonie@linaro.org>
ARM: bcm2835: enable USB_DWC2_HOST in defconfig

It broke when host was moved into a separate module, in 47a1685 ("usb:
dwc2/s3c-hsotg: move s3c-hsotg into dwc2 directory"),

Signed-off-by: Lubomir Rintel <lkundrak@v3.sk>
MMC: added alternative MMC driver