fdt: ARM: Add device tree control of U-Boot (CONFIG_OF_CONTROL)

This adds a device tree pointer to the global data. It can be set by
board code. A later commit will add support for making a device
tree binary blob available to U-Boot for run-time configuration.

Signed-off-by: Simon Glass <sjg@chromium.org>

README

@@ -816,6 +816,17 @@ The following options need to be configured:
 
 		XXX - this list needs to get updated!
 
+- Device tree:
+		CONFIG_OF_CONTROL
+		If this variable is defined, U-Boot will use a device tree
+		to configure its devices, instead of relying on statically
+		compiled #defines in the board file. This option is
+		experimental and only available on a few boards. The device
+		tree is available in the global data as gd->fdt_blob.
+
+		U-Boot needs to get its device tree from somewhere. This will
+		be enabled in a future patch.
+
 - Watchdog:
 		CONFIG_WATCHDOG
 		If this variable is defined, it enables watchdog

arch/arm/include/asm/global_data.h

@@ -76,6 +76,7 @@ typedef	struct	global_data {
 #if !(defined(CONFIG_SYS_ICACHE_OFF) && defined(CONFIG_SYS_DCACHE_OFF))
 	unsigned long	tlb_addr;
 #endif
+	const void	*fdt_blob;	/* Our device tree, NULL if none */
 	void		**jt;		/* jump table */
 	char		env_buf[32];	/* buffer for getenv() before reloc. */
 #if defined(CONFIG_POST) || defined(CONFIG_LOGBUFFER)