Add support for devices with less than 3 lines on the LCD.

(closes issue #17600)
Reported by: minaguib
Patches:
      ast_unistim_height_v2.patch uploaded by minaguib (license 1078)
Tested by: minaguib


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@275466 65c4cc65-6c06-0410-ace0-fbb531ad65f3