Add a remoteproc driver for OMAP4, so we can boot the dual-M3 and
and DSP subsystems.

Use the omap_device_* API to control the hardware state, and utilize
the OMAP mailbox to interrupt the remote processor when a new message
is pending (the mailbox payload is used to tell it which virtqueue was
the message placed in).

Conversely, when an inbound mailbox message arrives, tell the remoteproc
core which virtqueue is triggered.

Later we will also use the mailbox payload to signal omap-specific
events like remote crashes (which will be used to trigger remoteproc
recovery) and power management transitions. At that point we will also
extend the remoteproc core to support this.

Based on (but now quite far from) work done by Fernando Guzman Lugo
<fernando.lugo@ti.com> and Hari Kanigeri <h-kanigeri2@ti.com>.

Designed with Brian Swetland <swetland@google.com>.
Signed-off-by: Ohad Ben-Cohen <ohad@wizery.com>
Acked-by: Tony Lindgren <tony@atomide.com>
Cc: Brian Swetland <swetland@google.com>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Grant Likely <grant.likely@secretlab.ca>
Cc: Russell King <linux@arm.linux.org.uk>
Cc: Rusty Russell <rusty@rustcorp.com.au>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Greg KH <greg@kroah.com>
Cc: Stephen Boyd <sboyd@codeaurora.org>