drm: bridge: Generalize Exynos-DSI driver into a Samsung DSIM bridge

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

In order to access this DSI controller between various platform SoCs,
the ideal way to incorporate this in the drm stack is via the drm bridge
driver.

We already have a consolidated code for supporting component and bridge
based DRM drivers, so keep the exynos component based code in existing
exynos_drm_dsi.c and move generic bridge code as part of samsung-dsim.c

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