drm/exynos: fimd: add HW trigger support

This patch adds HW trigger support on i80 mode.

Until now, Exynos DRM only supported SW trigger which was set
SWTRGCMD bit of TRIGCON register by CPU to transfer scanout
buffer to Display bus device or panel.

With this patch, the transmission to Display bus device or
panel will be initiated by FIMD controller.

Signed-off-by: Inki Dae <inki.dae@samsung.com>