[media] s5p-g2d: Add DT based discovery support

This patch adds device tree based discovery support to the G2D driver.

Signed-off-by: Sachin Kamat <sachin.kamat@linaro.org>
Signed-off-by: Sylwester Nawrocki <s.nawrocki@samsung.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>