Convert CONFIG_SYS_SPL_ARGS_ADDR to Kconfig

This converts the following to Kconfig:
   CONFIG_SYS_SPL_ARGS_ADDR

In doing so, we also consistently use this variable for SPL_OS_BOOT and
not CONFIG_SYS_FDT_BASE in some cases.

Signed-off-by: Tom Rini <trini@konsulko.com>
diff --git a/common/spl/Kconfig b/common/spl/Kconfig
index dfbda1b..71b2600 100644
--- a/common/spl/Kconfig
+++ b/common/spl/Kconfig
@@ -1188,6 +1188,14 @@
 	  Enable booting directly to an OS from SPL.
 	  for more info read doc/README.falcon
 
+config SYS_SPL_ARGS_ADDR
+	hex "Address in memory to load 'args' file for Falcon Mode to"
+	depends on SPL_OS_BOOT
+	default 0x88000000 if ARCH_OMAP2PLUS
+	help
+	  Address in memory where the 'args' file, typically a device tree
+	  will be loaded in to memory.
+
 if SPL_OS_BOOT
 config SYS_OS_BASE
 	hex "addr, where OS is found"