Support scaled output for non-FHD screen

This is a quick hack supporting scaled output to fit various
monitors which has not FHD screen resolution.
(Especially useful for running CES2017 demo on QEMU)

 - Layer
   - source rectangle is 1080x1920
   - destination rectangle is variable to fit screen resolution
 - Surface
   - source rectangle is based 1080x1920
   - destination rectangle is based 1080x1920
 - From application view
   - screen size is always 1080x1920 and does not need
     to care about phsycial screen size

This change enables scaled output which changes the size
according to the ratio of source and destination region
of homescreen layer.

This patch doesn't resolve an issue, 'CES2017 demo keep blank
screen after booting on some platform (QEMU, Raspberry Pi3,
MinnowMax)'. (Workaround: just run any weayland client
application such as 'LayerManagerControl', 'qmlscene', or
weston example like 'weston-flower', then it breaks blank screen)

Signed-off-by: Tadao Tanikawa <tanikawa.tadao@jp.panasonic.com>