Derive display resolution from /dev/fb instead of hardcoded values

Open-webOS-DCO-1.0-Signed-off-by: Sapna Todwal <sapna.todwal@palm.com>

Change-Id: I185db273f2af7c371f6b63cd7edc679b99189065
Reviewed-on: http://g2g.palm.com/1512
Reviewed-by: Build Verification
Tested-by: Sapna Todwal <sapna.todwal@palm.com>
Reviewed-by: Keith Derrick <keith.derrick@palm.com>