greybus: arpc: move arpc definitions to their own header

Move the ARPC definitions to their own header.

ARPC is not part of greybus, but is rather an implementation-specific
means of communicating with a certain class of host-device hardware.

Note that the same is true for the APBA USB vendor requests, but we keep
them in the greybus header for the time being.

Signed-off-by: Johan Hovold <johan@hovoldconsulting.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>
diff --git a/drivers/staging/greybus/es2.c b/drivers/staging/greybus/es2.c
index 996cfc6..955b37d 100644
--- a/drivers/staging/greybus/es2.c
+++ b/drivers/staging/greybus/es2.c
@@ -14,6 +14,7 @@
 #include <linux/list.h>
 #include <asm/unaligned.h>
 
+#include "arpc.h"
 #include "greybus.h"
 #include "greybus_trace.h"
 #include "kernel_ver.h"