meta-phosphor: static-norootfs: use xz for small flash images

The 32MB flash machines typically do not have enough space to hold
a zstd compressed rootfs, so default them to use xz.

Signed-off-by: Patrick Williams <patrick@stwcx.xyz>
Change-Id: I6f24d771e41853c13ec55c9a35bc5dff3f523cb2
diff --git a/meta-phosphor/conf/machine/include/image-type/static-norootfs.inc b/meta-phosphor/conf/machine/include/image-type/static-norootfs.inc
index 02574da..a966c94 100644
--- a/meta-phosphor/conf/machine/include/image-type/static-norootfs.inc
+++ b/meta-phosphor/conf/machine/include/image-type/static-norootfs.inc
@@ -1,4 +1,5 @@
 INITRAMFS_CTYPE="zst"
+INITRAMFS_CTYPE:flash-32768="xz"
 
 IMAGE_FSTYPES += "cpio.${INITRAMFS_CTYPE}.fitImage mtd-static-norootfs"