linux: Only run depmod during the finalize hook

Commit 82e7656400 ("linux: Allow modprobe for out-of-tre modules") added
support for running depmod as part of the target finalize hook.

However, it also originally set DEPMOD to /dev/null, a hunk that was
removed upon apply. The kernel depmod wrapper script uses `command` to
verify that whatever is passed into DEPMOD is known to the shell.
These days if the DEPMOD tool is set to something incorrect the depmod
script will just warn [1], but there are trees where the depmod script will
stop with a hard error. [2]

Running depmod as part of out-of-tree module installations causes
unnecessary files to be generated and installed.

Since we're already running depmod in the finalize hook, stub this call to
`true` as it's definitely a shell callable, and it will always succeed.
This is what is done for other packaging scripts in the kernel tree. [3]

Link: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/scripts/depmod.sh?id=914b087ff9e0e9a399a4927fa30793064afc0178 [1]
Link: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/scripts/depmod.sh?id=934193a654c1f4d0643ddbf4b2529b508cae926e [2]
Link: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/scripts/package/PKGBUILD?id=8bdd53e066012bed431667393676d1b5e8cce153#n70 [3]
Signed-off-by: John Ernberg <j@j-ernberg.se>
Signed-off-by: Arnout Vandecappelle <arnout@rnout.be>

linux/linux.mk

@@ -164,7 +164,7 @@ LINUX_MAKE_FLAGS = \
 	CROSS_COMPILE="$(TARGET_CROSS)" \
 	WERROR=0 \
 	REGENERATE_PARSERS=1 \
-	DEPMOD=$(HOST_DIR)/sbin/depmod
+	DEPMOD=true
 
 ifeq ($(BR2_REPRODUCIBLE),y)
 LINUX_MAKE_ENV += \