Convert CONFIG_SYS_NAND_SPL_KERNEL_OFFS to Kconfig

This converts the following to Kconfig:
   CONFIG_SYS_NAND_SPL_KERNEL_OFFS

Signed-off-by: Tom Rini <trini@konsulko.com>
diff --git a/common/spl/Kconfig b/common/spl/Kconfig
index 71b2600..05049c1 100644
--- a/common/spl/Kconfig
+++ b/common/spl/Kconfig
@@ -1196,6 +1196,10 @@
 	  Address in memory where the 'args' file, typically a device tree
 	  will be loaded in to memory.
 
+config SYS_NAND_SPL_KERNEL_OFFS
+	hex "Address in memory to load the OS file for Falcon mode to"
+	depends on SPL_OS_BOOT && SPL_NAND_SUPPORT
+
 if SPL_OS_BOOT
 config SYS_OS_BASE
 	hex "addr, where OS is found"