greybus: create host-device compilation unit

Move everything host-device related to hd.c and hd.h.

Signed-off-by: Johan Hovold <johan@hovoldconsulting.com>
Reviewed-by: Viresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>
diff --git a/drivers/staging/greybus/Makefile b/drivers/staging/greybus/Makefile
index b8dc36b..ba60430 100644
--- a/drivers/staging/greybus/Makefile
+++ b/drivers/staging/greybus/Makefile
@@ -1,5 +1,6 @@
 greybus-y :=	core.o		\
 		debugfs.o	\
+		hd.o		\
 		manifest.o	\
 		endo.o		\
 		module.o	\