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_SPIFLASH_defconfig b/configs/BSC9131RDB_SPIFLASH_defconfig
index 178618c..ebb41d2 100644
--- a/configs/BSC9131RDB_SPIFLASH_defconfig
+++ b/configs/BSC9131RDB_SPIFLASH_defconfig
@@ -25,3 +25,4 @@
 CONFIG_USB=y
 CONFIG_USB_STORAGE=y
 CONFIG_OF_LIBFDT=y
+CONFIG_FDT_FIXUP_PARTITIONS=y