wic: search nonarch STAGING_DATADIR for multilib

It fails to build multilib image such as lib32-core-image-minimal with
wic by set 'IMAGE_FSTYPES = "wic"':

| ERROR: Couldn't find correct bootimg_dir, exiting

When multilib is enabled, STAGING_DATADIR is expanded with MLPREFIX. But
dependencies of images such as syslinux is still populated to nonarch
STAGING_DATADIR.

Search nonarch STAGING_DATADIR to fix the error.

(From OE-Core rev: dbae9a6f9a1c6cc7d4dd680d7bbda3dfa40f3491)

Signed-off-by: Kai Kang <kai.kang@windriver.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

scripts/lib/wic/plugins/source/bootimg-pcbios.py

@@ -26,6 +26,7 @@
 
 import logging
 import os
+import re
 
 from wic import WicError
 from wic.engine import get_custom_config
@@ -47,10 +48,17 @@ class BootimgPcbiosPlugin(SourcePlugin):
         """
         Check if dirname exists in default bootimg_dir or in STAGING_DIR.
         """
-        for result in (bootimg_dir, get_bitbake_var("STAGING_DATADIR")):
+        staging_datadir = get_bitbake_var("STAGING_DATADIR")
+        for result in (bootimg_dir, staging_datadir):
             if os.path.exists("%s/%s" % (result, dirname)):
                 return result
 
+        # STAGING_DATADIR is expanded with MLPREFIX if multilib is enabled
+        # but dependency syslinux is still populated to original STAGING_DATADIR
+        nonarch_datadir = re.sub('/[^/]*recipe-sysroot', '/recipe-sysroot', staging_datadir)
+        if os.path.exists(os.path.join(nonarch_datadir, dirname)):
+            return nonarch_datadir
+
         raise WicError("Couldn't find correct bootimg_dir, exiting")
 
     @classmethod