kernel: fix rootfs initramfs not updating on subsequent single build

There is currently a problem where the rootfs in an initramfs image for
single target build is not updated on subsequent run. This is caused by
a bug introduced in d78dec3e19e3 ("kernel: copy kernel build dir on
Per-Device Initramfs compilation") where the initramfs_data.cpio rm was
moved to PrepareConfigPerRootfs. This caused the side effect of dropping
the rm call for single target build making the kernel reusing the
previous generated initramfs_data.cpio.

To correctly handle this, restore the original location of this call
right after the touch /init call. This way the kernel will always
regenerate the initramfs embedded rootfs ALSO for single target build.

Fixes: d78dec3e19e3 ("kernel: copy kernel build dir on Per-Device Initramfs compilation")
Signed-off-by: Christian Marangi <[email protected]>
(cherry picked from commit 334c649a8d9b191c0282f9104b3997b090628f56)

include/kernel-defaults.mk

@@ -175,7 +175,6 @@ define Kernel/PrepareConfigPerRootfs
 		[ ! -d "$(1)" ] || rm -rf $(1); \
 		mkdir $(1) && $(CP) -T $(LINUX_DIR) $(1); \
 		touch $(1)/.config; \
-		rm -rf $(1)/usr/initramfs_data.cpio*; \
 	}
 endef
 
@@ -190,6 +189,7 @@ define Kernel/CompileImage/Initramfs
 		$(call Kernel/Configure/Initramfs,$(if $(1),$(1),$(TARGET_DIR)),$(LINUX_DIR)$(2)); \
 		$(CP) $(GENERIC_PLATFORM_DIR)/other-files/init $(if $(1),$(1),$(TARGET_DIR))/init; \
 		$(if $(SOURCE_DATE_EPOCH),touch -hcd "@$(SOURCE_DATE_EPOCH)" $(if $(1),$(1),$(TARGET_DIR)) $(if $(1),$(1),$(TARGET_DIR))/init;) \
+		rm -rf $(LINUX_DIR)$(2)/usr/initramfs_data.cpio*; \
 		$(if $(CONFIG_TARGET_ROOTFS_INITRAMFS_SEPARATE), \
 			$(call locked,{ \
 				$(if $(call qstrip,$(CONFIG_EXTERNAL_CPIO)), \