README.qemu: qemuppc64 is not supported

(From OE-Core rev: 3b413a80578caacd9a7f405f3c51a3921d78a60d)

Signed-off-by: Randy MacLeod <Randy.MacLeod@windriver.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

README.qemu

@@ -7,7 +7,7 @@ are currently supported in 32 and 64 bit variants:
 
   * ARM (qemuarm + qemuarm64)
   * x86 (qemux86 + qemux86-64)
-  * PowerPC (qemuppc + qemuppc64)
+  * PowerPC (qemuppc only)
   * MIPS (qemumips + qemumips64)
 
 Use of the QEMU images is covered in the Yocto Project Reference Manual.