xf86-video-imxfb-vivante: Adapt code to new types used in Xserver 1.16

The new Xserver 1.16 version has some changes which causes some
compilation warning, this patch adapts the EXA driver for this
changes.

Signed-off-by: Prabhu Sundararaj <prabhu.sundararaj@freescale.com>
Signed-off-by: Otavio Salvador <otavio@ossystems.com.br>