Blackfin arch: split board selection off into mach subdirs

Signed-off-by: Mike Frysinger <michael.frysinger@analog.com>
Signed-off-by: Bryan Wu <bryan.wu@analog.com>

diff --git a/arch/blackfin/mach-bf537/Kconfig b/arch/blackfin/mach-bf537/Kconfig
index e6648db..8255374 100644
--- a/arch/blackfin/mach-bf537/Kconfig
+++ b/arch/blackfin/mach-bf537/Kconfig
@@ -1,5 +1,7 @@
 if (BF537 || BF534 || BF536)
 
+source "arch/blackfin/mach-bf537/boards/Kconfig"
+
 menu "BF537 Specific Configuration"
 
 comment "Interrupt Priority Assignment"