openrisc: remove CONFIG_SYMBOL_PREFIX

Remove the SYMBOL_PREFIX Kconfig symbol as it's empty anyway.
Signed-off-by: NJames Hogan <james.hogan@imgtec.com>
Cc: Jonas Bonn <jonas@southpole.se>
Cc: linux@lists.openrisc.net
Cc: Mike Frysinger <vapier@gentoo.org>
Signed-off-by: NJonas Bonn <jonas@southpole.se>

arch/openrisc/Kconfig

@@ -26,10 +26,6 @@ config OPENRISC
 config MMU
 	def_bool y
 
-config SYMBOL_PREFIX
-        string
-        default ""
-
 config HAVE_DMA_ATTRS
 	def_bool y