spl: move FDT_FIXUP_PARTITIONS to Kconfig

Move FDT_FIXUP_PARTITIONS to Kconfig and cleanup existing
uses.

Signed-off-by: Heiko Schocher <hs@denx.de>
diff --git a/configs/BSC9131RDB_NAND_defconfig b/configs/BSC9131RDB_NAND_defconfig
index ad00622..46b5b8e 100644
--- a/configs/BSC9131RDB_NAND_defconfig
+++ b/configs/BSC9131RDB_NAND_defconfig
@@ -28,3 +28,4 @@
 CONFIG_USB=y
 CONFIG_USB_STORAGE=y
 CONFIG_OF_LIBFDT=y
+CONFIG_FDT_FIXUP_PARTITIONS=y