Retrieve FW version from IMG_BUILTIN_DIR

Added method to retrieve firmware level found in IMG_BUILTIN_DIR. This
is required behavior on some systems types.

Tested:
  Installed openbmc image on system and verified the function returns
  the version available in IMG_BUILT_DIR.

Change-Id: I10166a1412fb9de421bd304c40916a81c1ca0558
Signed-off-by: Faisal Awada <faisal@us.ibm.com>
diff --git a/meson.options b/meson.options
index f37d08d..b5877c9 100644
--- a/meson.options
+++ b/meson.options
@@ -58,3 +58,8 @@
        type: 'string',
        value: '/usr/share/obmc/psu',
        description: 'The read-only directory where the built-in PSU images are stored')
+
+option('ALWAYS_USE_BUILTIN_IMG_DIR',
+    type: 'boolean',
+    value: false,
+    description: 'Only scan for PSU images in IMG_BUILTIN_DIR')