nios2: add kgdb support

Signed-off-by: Ley Foon Tan <lftan@altera.com>
diff --git a/arch/nios2/Kconfig b/arch/nios2/Kconfig
index f77991e..4375554 100644
--- a/arch/nios2/Kconfig
+++ b/arch/nios2/Kconfig
@@ -8,6 +8,7 @@
 	select GENERIC_IRQ_PROBE
 	select GENERIC_IRQ_SHOW
 	select HAVE_ARCH_TRACEHOOK
+	select HAVE_ARCH_KGDB
 	select IRQ_DOMAIN
 	select MODULES_USE_ELF_RELA
 	select OF