dt-bindings: phy: samsung,mipi-video-phy: document exynos7870 MIPI phy

The Exynos7870 MIPI PHY device contains one DSIM PHY block and three
CSIS PHY blocks. It also requires two sysregs, one for display, and the
other for cameras. Document this device.

Signed-off-by: Kaustabh Chakraborty <kauschluss@disroot.org>
Acked-by: Conor Dooley <conor.dooley@microchip.com>
Link: https://lore.kernel.org/r/20250612-exynos7870-mipi-phy-v1-1-3fff0b62d9d3@disroot.org


Signed-off-by: Vinod Koul <vkoul@kernel.org>