bootflow: bootmeth_efi: Handle fdt not available.

While booting with efi, if fdt isn't available externally,
just use the built-in one.

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

Signed-off-by: Shantur Rathore <i@shantur.com>

include/bootflow.h

@@ -45,10 +45,12 @@ enum bootflow_state_t {
  *	CONFIG_OF_HAS_PRIOR_STAGE is enabled
  * @BOOTFLOWF_STATIC_BUF: Indicates that @bflow->buf is statically set, rather
  *	than being allocated by malloc().
+ * @BOOTFLOWF_USE_BUILTIN_FDT : Indicates that current bootflow uses built-in FDT
  */
 enum bootflow_flags_t {
 	BOOTFLOWF_USE_PRIOR_FDT	= 1 << 0,
 	BOOTFLOWF_STATIC_BUF	= 1 << 1,
+	BOOTFLOWF_USE_BUILTIN_FDT	= 1 << 2,
 };
 
 /**