drm: exynos: dsi: Introduce hw_type platform data

Samsung MIPI DSIM controller is common DSI IP that can be used
in various SoCs like Exynos, i.MX8M Mini/Nano/Plus.

Add hw_type enum via platform_data so that accessing the different
controller data between various platforms becomes easy and meaningful.

Tested-by: Marek Szyprowski <m.szyprowski@samsung.com>
Reviewed-by: Marek Vasut <marex@denx.de>
Reviewed-by: Frieder Schrempf <frieder.schrempf@kontron.de>
Suggested-by: Marek Szyprowski <m.szyprowski@samsung.com>
Signed-off-by: Jagan Teki <jagan@amarulasolutions.com>
Signed-off-by: Inki Dae <inki.dae@samsung.com>