Blackfin: unify bootmode based LDR_FLAGS setup

Unify this convention for all Blackfin boards.

Signed-off-by: Mike Frysinger <vapier@gentoo.org>
diff --git a/board/bf537-minotaur/config.mk b/board/bf537-minotaur/config.mk
index 0f0ed48..f7aa8ef 100644
--- a/board/bf537-minotaur/config.mk
+++ b/board/bf537-minotaur/config.mk
@@ -26,5 +26,4 @@
 CONFIG_BFIN_CPU = bf537-0.2
 
 # Set some default LDR flags based on boot mode.
-LDR_FLAGS-BFIN_BOOT_UART       := --port g --gpio 6
-LDR_FLAGS += $(LDR_FLAGS-$(CONFIG_BFIN_BOOT_MODE))
+LDR_FLAGS-BFIN_BOOT_UART := --port g --gpio 6