boot/barebox, package/linux-headers: carry site-method archive format version when overriding _SOURCE

Commit 5b95a5dc2 (support/download: change format of archives generated
from git) changed the way the archives generated from git repositories
are named, adding a "format-version" identifier right between the
package version and the file extension.

Commit c043ecb20 (support/download: change format of archives generated
from svn) did so for archives generated from a subversion checkout.

However, for a few packages, we manually force the _SOURCE variable,
because we want to share the archive with another package, to avoid
downloading and storing those archives twice. This is the case for:

  - linux-headers and linux
  - barebox-aux and barebox

When the generated tarballs were renamed with the aforementioned
commits, those packages were not updated accordingly.

Fix that by manually propagating the per-site-method format-version.

Reported-by: "Stephane Viau (OSS)" <stephane.viau@oss.nxp.com>
Signed-off-by: Yann E. MORIN <yann.morin.1998@free.fr>
Cc: "Stephane Viau (OSS)" <stephane.viau@oss.nxp.com>
Cc: Arnout Vandecappelle <arnout@mind.be>
Cc: Thomas Petazzoni <thomas.petazzoni@bootlin.com>
Cc: Peter Korsgaard <peter@korsgaard.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>

boot/barebox/barebox.mk

@@ -28,7 +28,7 @@ $(1)_SITE_METHOD = git
 # Override the default value of _SOURCE to 'barebox-*' so that it is not
 # downloaded a second time for barebox-aux; also alows avoiding the hash
 # check:
-$(1)_SOURCE = barebox-$$($(1)_VERSION).tar.gz
+$(1)_SOURCE = barebox-$$($(1)_VERSION)$$(BR_FMT_VERSION_git).tar.gz
 else
 # Handle stable official Barebox versions
 $(1)_SOURCE = barebox-$$($(1)_VERSION).tar.bz2