Keyguard: Show backdrop when sim pin secure screen shown

Devices that support bluring remove FLAG_SHOW_WALLPAPER from the
layout params flags which causes the foreground activity to be
completely visible when the sim pin security screen is shown.  If
this screen is visible we treat it as if the keyguard is visible and
show the backdrop if available, otherwise it is blurred.

Change-Id: Ifeae28816cc2f1fad30a2edf1cf51d5cabb005e9
TICKET: CYNGNOS-1266