Convert CONFIG_BUILD_TARGET to Kconfig

This converts the following to Kconfig:
   CONFIG_BUILD_TARGET

Signed-off-by: Tom Rini <trini@konsulko.com>
diff --git a/include/configs/db-88f6281-bp.h b/include/configs/db-88f6281-bp.h
index cc51e66..e234b0b 100644
--- a/include/configs/db-88f6281-bp.h
+++ b/include/configs/db-88f6281-bp.h
@@ -11,7 +11,6 @@
 #define CONFIG_SKIP_LOWLEVEL_INIT	/* disable board lowlevel_init */
 #define CONFIG_SYS_TCLK		166666667
 #define CONFIG_SYS_KWD_CONFIG	$(CONFIG_BOARDDIR)/kwbimage.cfg
-#define CONFIG_BUILD_TARGET	"u-boot.kwb"
 
 /* additions for new ARM relocation support */
 #define CONFIG_SYS_SDRAM_BASE	0x00000000