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/lib/Kconfig b/lib/Kconfig
index 16ff01a..0e0d8ef 100644
--- a/lib/Kconfig
+++ b/lib/Kconfig
@@ -154,6 +154,15 @@
 	  particular compatible nodes. The library operates on a flattened
 	  version of the device tree.
 
+config FDT_FIXUP_PARTITIONS
+	bool "overwrite MTD partitions in DTS through defined in 'mtdparts'"
+	depends on OF_LIBFDT
+	default n
+	help
+	  Allow overwriting defined partitions in the device tree blob
+	  using partition info defined in the 'mtdparts' environment
+	  variable.
+
 source lib/efi/Kconfig
 source lib/efi_loader/Kconfig