Check and fail early if requested wallpaper size exceeds maximum texture size.

This fixes an issue where OpenGL initialization succeeds but buffer allocation fails because the requested wallpaper size
is too large (or otherwise unsupported) by the graphics hardware. This fixes an issue where SystemUI crashes constantly
on the PandaBoard when connected to a full HD display. Tested only on PandaBoard, no access to alternative hardware.
Signed-off-by: Wim Vander Schelden <wim.vander.schelden@philips.com>

Change-Id: I8d2e1ae9fd9772977c4e365f23f2f58bbca3787c