Blackfin: move KGDB selection to the way other arches do it

Signed-off-by: Mike Frysinger <vapier@gentoo.org>
diff --git a/arch/blackfin/Kconfig b/arch/blackfin/Kconfig
index 3123aa4..ed339b8 100644
--- a/arch/blackfin/Kconfig
+++ b/arch/blackfin/Kconfig
@@ -23,6 +23,7 @@
 
 config BLACKFIN
 	def_bool y
+	select HAVE_ARCH_KGDB
 	select HAVE_FUNCTION_GRAPH_TRACER
 	select HAVE_FUNCTION_TRACER
 	select HAVE_FUNCTION_TRACE_MCOUNT_TEST