greybus: arche-apb-ctrl: Add APB control driver

It was messy to integrate both SVC, APB (and any other arche
platform specific control) into one single driver. Especially
due to cross-dependency.

AP first needs to bringup SVC, as SVC should enable clock to APB.
APB should come up before HUB, as due to some reason HUB wouldn't
enumerate APB's is APB comes up later.
And on top of that we should have clean picture of hardware description
in DT file.

So this patch introduces APB control driver. Mostly copied from original
arche-platform driver + fixed boot sequence.
Signed-off-by: Vaibhav Hiremath <vaibhav.hiremath@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>

drivers/staging/greybus/Makefile

@@ -29,6 +29,7 @@ gb-raw-y := raw.o
 gb-hid-y := hid.o
 gb-es2-y := es2.o
 gb-arche-y := arche-platform.o
+gb-arche-apb-ctrl-y := arche-apb-ctrl.o
 gb-audio-codec-y := audio-codec.o
 gb-camera-y := camera.o
 
@@ -42,6 +43,7 @@ obj-m += gb-hid.o
 obj-m += gb-raw.o
 obj-m += gb-es2.o
 obj-m += gb-arche.o
+obj-m += gb-arche-apb-ctrl.o
 obj-m += gb-audio-codec.o
 obj-m += gb-camera.o