add LDPI assets to Phone.apk

CM9 Phone app does not support LDPI screens and crashes out when used
on an LDPI device. Not sure why since the system should be able to
resize assets to the current device. This overlay fixes it by adding
LDPI assets that the system will use on such devices.

Change-Id: I8a03b9a8f40ddeaeea64050bce77932a1ce48923