Convert CONFIG_SYS_FDT_PAD to Kconfig

This converts the following to Kconfig:
   CONFIG_SYS_FDT_PAD

Signed-off-by: Tom Rini <trini@konsulko.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
diff --git a/lib/Kconfig b/lib/Kconfig
index e888c29..6121c80 100644
--- a/lib/Kconfig
+++ b/lib/Kconfig
@@ -744,6 +744,16 @@
 	help
 	  This enables the FDT library (libfdt) overlay support.
 
+config SYS_FDT_PAD
+	hex "Maximum size of the FDT memory area passeed to the OS"
+	depends on OF_LIBFDT
+	default 0x13000 if FMAN_ENET || QE || U_QE
+	default 0x3000
+	help
+	  During OS boot, we allocate a region of memory within the bootmap
+	  for the FDT. This is the size that we will expand the FDT that we
+	  are using will be extended to be, in bytes.
+
 config SPL_OF_LIBFDT
 	bool "Enable the FDT library for SPL"
 	depends on SPL_LIBGENERIC_SUPPORT