remoteproc: add Kconfig menu

Add a dedicated Kconfig menu for the remoteproc drivers, so they
don't show up in the main driver menu.
Signed-off-by: Ohad Ben-Cohen <ohad@wizery.com>

drivers/remoteproc/Kconfig

+menu "Remoteproc drivers"
+
 # REMOTEPROC gets selected by whoever wants it
 config REMOTEPROC
 	tristate
@@ -22,3 +24,5 @@ config OMAP_REMOTEPROC
 
 	  It's safe to say n here if you're not interested in multimedia
 	  offloading or just want a bare minimum kernel.
+
+endmenu