kbuild: initramfs cleanup, set target from Kconfig

Rather than keep a list of all possible compression types in the
Makefile, set the target explicitly from Kconfig.
Reviewed-by: Francisco Blas Izquierdo Riera (klondike) <klondike@klondike.es>
Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

usr/Makefile

@@ -6,7 +6,9 @@ klibcdirs:;
 PHONY += klibcdirs
 
 suffix_y = $(subst $\",,$(CONFIG_INITRAMFS_COMPRESSION))
-AFLAGS_initramfs_data.o += -DINITRAMFS_IMAGE="usr/initramfs_data.cpio$(suffix_y)"
+datafile_y = initramfs_data.cpio$(suffix_y)
+AFLAGS_initramfs_data.o += -DINITRAMFS_IMAGE="usr/$(datafile_y)"
+
 
 # Generate builtin.o based on initramfs_data.o
 obj-$(CONFIG_BLK_DEV_INITRD) := initramfs_data.o
@@ -14,7 +16,7 @@ obj-$(CONFIG_BLK_DEV_INITRD) := initramfs_data.o
 # initramfs_data.o contains the compressed initramfs_data.cpio image.
 # The image is included using .incbin, a dependency which is not
 # tracked automatically.
-$(obj)/initramfs_data.o: $(obj)/initramfs_data.cpio$(suffix_y) FORCE
+$(obj)/initramfs_data.o: $(obj)/$(datafile_y) FORCE
 
 #####
 # Generate the initramfs cpio archive
@@ -38,10 +40,8 @@ endif
 quiet_cmd_initfs = GEN     $@
       cmd_initfs = $(initramfs) -o $@ $(ramfs-args) $(ramfs-input)
 
-targets := initramfs_data.cpio.gz initramfs_data.cpio.bz2 \
-	initramfs_data.cpio.lzma initramfs_data.cpio.xz \
-	initramfs_data.cpio.lzo initramfs_data.cpio.lz4 \
-	initramfs_data.cpio
+targets := $(datafile_y)
+
 # do not try to update files included in initramfs
 $(deps_initramfs): ;
 
@@ -51,6 +51,6 @@ $(deps_initramfs): klibcdirs
 # 2) There are changes in which files are included (added or deleted)
 # 3) If gen_init_cpio are newer than initramfs_data.cpio
 # 4) arguments to gen_initramfs.sh changes
-$(obj)/initramfs_data.cpio$(suffix_y): $(obj)/gen_init_cpio $(deps_initramfs) klibcdirs
+$(obj)/$(datafile_y): $(obj)/gen_init_cpio $(deps_initramfs) klibcdirs
 	$(Q)$(initramfs) -l $(ramfs-input) > $(obj)/.initramfs_data.cpio.d
 	$(call if_changed,initfs)