fs/cpio: add zstd as compression option

U-Boot mkimage zstd is available since v2020.10:
https://gitlab.denx.de/u-boot/u-boot/-/commit/26073f9ed3ab0aaf3c2a2b433fecb30a95a067d6

Signed-off-by: José Luis Salvador Rufo <salvador.joseluis@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>

fs/common.mk

@@ -154,6 +154,11 @@ ifeq ($(BR2_REPRODUCIBLE),)
 ROOTFS_$(2)_COMPRESS_CMD += -T $(PARALLEL_JOBS)
 endif
 endif
+ifeq ($(BR2_TARGET_ROOTFS_$(2)_ZSTD),y)
+ROOTFS_$(2)_DEPENDENCIES += host-zstd
+ROOTFS_$(2)_COMPRESS_EXT = .zst
+ROOTFS_$(2)_COMPRESS_CMD = zstd -19 -z -f -T$(PARALLEL_JOBS)
+endif
 
 $$(BINARIES_DIR)/$$(ROOTFS_$(2)_FINAL_IMAGE_NAME): ROOTFS=$(2)
 $$(BINARIES_DIR)/$$(ROOTFS_$(2)_FINAL_IMAGE_NAME): FAKEROOT_SCRIPT=$$(ROOTFS_$(2)_DIR)/fakeroot

fs/cpio/Config.in

@@ -51,6 +51,11 @@ config BR2_TARGET_ROOTFS_CPIO_XZ
 	help
 	  Do compress the cpio filesystem with xz.
 
+config BR2_TARGET_ROOTFS_CPIO_ZSTD
+	bool "zstd"
+	help
+	  Do compress the cpio filesystem with zstd.
+
 endchoice
 
 config BR2_TARGET_ROOTFS_CPIO_UIMAGE