runqemu: simplify checking for iso and ramfs

(From OE-Core rev: 69a1fca4374797dea56035ce56a17441a2ca9280)

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

scripts/runqemu-internal

@@ -593,12 +593,12 @@ if [ "$MACHINE" = "qemuzynq" ]; then
     fi
 fi
 
-if [ "x$RAMFS" = "xtrue" ]; then
+if [ "$FSTYPE" = "cpio.gz" ]; then
     QEMUOPTIONS="-initrd $ROOTFS -nographic"
     KERNCMDLINE="root=/dev/ram0 console=ttyS0 debugshell"
 fi
 
-if [ "x$ISOFS" = "xtrue" ]; then
+if [ "$FSTYPE" = "iso" ]; then
     QEMUOPTIONS="$QEMU_NETWORK_CMD -cdrom $ROOTFS $QEMU_UI_OPTIONS"
 fi