ARM: dts: rcar-gen2: Add reset control properties

Hi Simon, Magnus,

This patch series describes the reset topology on all R-Car Gen2 Socs, like was done before for R-Car Gen3 and RZ/G1.

Resets usually match the corresponding module clocks. Exceptions are:
- The audio module has resets for the Serial Sound Interfaces only,
- The display module has only a single reset for all DU channels, but adding reset properties for the display is postponed upon request from Laurent.

Note that this patch series contains hardware description only. Actual reset policy is to be defined and implemented separately. Also, this is an optional feature, to be enabled explicitly using CONFIG_RESET_CONTROLLER=y. When enabled, an on-SoC device can be reset easily using device_reset(), or by using the reset_control_*() API when more fine-grained control is desired.

Possible use cases are (not exhaustive):
- Reset a device before use, to make sure it's in a predefined state, and doesn't depend on earlier configuration by e.g. the boot loader,
- Reset a device after detecting an anomaly,
- Reset a device to verify suspend/resume is handled correctly by the driver in case the device would be part of a power domain on a different/future SoC.

This has been tested on r8a7790/lager, r8a7791/koelsch, r8a7792/blanche, and r8a7794/alt (r8a7793/gose was offline).

Thanks for applying!

Geert Uytterhoeven (5):
ARM: dts: r8a7790: Add reset control properties
ARM: dts: r8a7791: Add reset control properties
ARM: dts: r8a7792: Add reset control properties
ARM: dts: r8a7793: Add reset control properties
ARM: dts: r8a7794: Add reset control properties