runqemu: let ramfs equal to cpio.gz

For example, support both:
$ runqemu qemux86-64 ramfs
$ runqemu qemux86-64 cpio.gz (new)

(From OE-Core rev: 6529264776701d4f5a1e4a8336ac2e01a6ddea85)

Signed-off-by: Robert Yang <liezhi.yang@windriver.com>
Signed-off-by: Ross Burton <ross.burton@intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

scripts/runqemu

@@ -40,7 +40,7 @@ Examples:
   $MYNAME qemux86-64 core-image-sato ext4
   $MYNAME qemux86-64 wic-image-minimal wic
   $MYNAME path/to/bzImage-qemux86.bin path/to/nfsrootdir/ serial
-  $MYNAME qemux86 iso/hddimg/vmdk/qcow2/vdi/ramfs...
+  $MYNAME qemux86 iso/hddimg/vmdk/qcow2/vdi/ramfs/cpio.gz...
   $MYNAME qemux86 qemuparams="-m 256"
   $MYNAME qemux86 bootparams="psplash=false"
   $MYNAME path/to/<image>-<machine>.vmdk
@@ -132,7 +132,7 @@ while true; do
             check_fstype_conflicts $arg
             IS_VM="true"
             ;;
-        "ramfs")
+        "ramfs" | "cpio.gz")
             FSTYPE=cpio.gz
             ;;
         "nographic")