initramfs: select builtin initram compression algorithm on KConfig instead of Makefile

Move the current builtin initram compression algorithm selection from
the Makefile into the INITRAMFS_COMPRESSION variable.  This makes
deciding algorithm precedence easier and would allow for overrides if
new algorithms want to be tested.

Link: http://lkml.kernel.org/r/57EAD769.1090401@klondike.es
Signed-off-by: Francisco Blas Izquierdo Riera (klondike) <klondike@klondike.es>
Cc: P J P <ppandit@redhat.com>
Cc: Paul Bolle <pebolle@tiscali.nl>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

usr/Kconfig

@@ -98,3 +98,13 @@ config RD_LZ4
 	help
 	  Support loading of a LZ4 encoded initial ramdisk or cpio buffer
 	  If unsure, say N.
+
+config INITRAMFS_COMPRESSION
+	string
+	default ".gz"   if RD_GZIP
+	default ".lz4"  if RD_LZ4
+	default ".lzo"  if RD_LZO
+	default ".xz"   if RD_XZ
+	default ".lzma" if RD_LZMA
+	default ".bz2"  if RD_BZIP2
+	default ""

usr/Makefile

@@ -5,25 +5,7 @@
 klibcdirs:;
 PHONY += klibcdirs
 
-
-# Bzip2
-suffix_$(CONFIG_RD_BZIP2)  = .bz2
-
-# Lzma
-suffix_$(CONFIG_RD_LZMA)   = .lzma
-
-# XZ
-suffix_$(CONFIG_RD_XZ)     = .xz
-
-# Lzo
-suffix_$(CONFIG_RD_LZO)    = .lzo
-
-# Lz4
-suffix_$(CONFIG_RD_LZ4)    = .lz4
-
-# Gzip
-suffix_$(CONFIG_RD_GZIP)   = .gz
-
+suffix_y = $(CONFIG_INITRAMFS_COMPRESSION)
 AFLAGS_initramfs_data.o += -DINITRAMFS_IMAGE="usr/initramfs_data.cpio$(suffix_y)"
 
 # Generate builtin.o based on initramfs_data.o