Use INITRAMFS_FSTYPES to build a u-boot ramdisk

do_generate_flash() was manually packaging the initramfs cpio archive as
a u-boot ramdisk legacy image.  Add the u-boot type to
INITRAMFS_FSTYPES to use the existing infrastructure instead.

NOTE: if you have an existing build directory, this change may cause the
build to fail while creating symlinks.  This is caused by the .u-boot
file changing from an actual file to a symlink.

Change-Id: I9fa69620f97452671f89675768b1d1f33dbe97f2
Signed-off-by: Rick Altherr <raltherr@google.com>
diff --git a/conf/machine/include/obmc-bsp-common.inc b/conf/machine/include/obmc-bsp-common.inc
index 3fe9e9f..e52d8a3 100644
--- a/conf/machine/include/obmc-bsp-common.inc
+++ b/conf/machine/include/obmc-bsp-common.inc
@@ -20,7 +20,7 @@
 IMAGE_CLASSES += "obmc-phosphor-image_types_uboot"
 
 INITRAMFS_CTYPE ?= "lzma"
-INITRAMFS_FSTYPES += "cpio.${INITRAMFS_CTYPE}"
+INITRAMFS_FSTYPES += "cpio.${INITRAMFS_CTYPE} cpio.${INITRAMFS_CTYPE}.u-boot"
 
 MACHINE_FEATURES_BACKFILL_CONSIDERED = "qemu-usermode"