bootstd: Support bootmeths which can scan any partition

Some bootmeths support scanning a partition without a filesystem on it.
Add a flag to support this.

This will allow the ChromiumOS bootmeth to find kernel partition, which
are stored in a special format, without a filesystem.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/include/bootmeth.h b/include/bootmeth.h
index d3d8d60..0fc3610 100644
--- a/include/bootmeth.h
+++ b/include/bootmeth.h
@@ -16,9 +16,12 @@
  * enum bootmeth_flags - Flags for bootmeths
  *
  * @BOOTMETHF_GLOBAL: bootmeth handles bootdev selection automatically
+ * @BOOTMETHF_ANY_PART: bootmeth is willing to check any partition, even if it
+ * has no filesystem
  */
 enum bootmeth_flags {
 	BOOTMETHF_GLOBAL	= BIT(0),
+	BOOTMETHF_ANY_PART	= BIT(1),
 };
 
 /**