phy: mtk-mipi-csi: add driver for CSI phy

This is a new driver that supports the MIPI CSI CD-PHY version 0.5

The number of PHYs depend on the SoC.
Each PHY can support D-PHY only or CD-PHY configuration.
The driver supports only D-PHY mode, so CD-PHY
compatible PHY are configured in D-PHY mode.

[Julien Stephan: simplify driver model: one instance per phy vs
one instance for all phys]

Signed-off-by: Louis Kuo <louis.kuo@mediatek.com>
Signed-off-by: Phi-bang Nguyen <pnguyen@baylibre.com>
[Julien Stephan: refactor code]
Co-developed-by: Julien Stephan <jstephan@baylibre.com>
Signed-off-by: Julien Stephan <jstephan@baylibre.com>
Reviewed-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Link: https://lore.kernel.org/r/20240111101738.468916-1-jstephan@baylibre.com
Signed-off-by: Vinod Koul <vkoul@kernel.org>