meta-shr: Restore HANDHELD_CVS variable

* these were correctly removed from oe-core in
  commit 3b333896c71689c664475d53daed52404bf6b21b
  Author: Phil Blundell <pb@pbcl.net>
  Date:   Thu Nov 14 18:15:46 2013 +0000

    bitbake.conf: Remove obsolete/unused MIRROR cruft
  but we still need them here, so add them to layer.conf

* HANDHELD_CVS is used by atd-over-fso recipe