phy: sun4i-usb: drop num_phys assumption

So far we set a number of expected Allwinner USB PHY instances for any
given compatible string, and would fail if we do not find every PHY
described properly in the DT (missing reset/PMU/clocks).
This is somewhat redundant, as the DT only describes the resources for
the implemented PHYs, but goes in line with being strict about firmware
descriptions, and rather fixing things in the driver code, based on the
compatible string.
However this causes issues when we make a mistake, like we did recently
on the A523: there are actually three USB PHYs, not two, as we assumed.
Changing the number in the driver and the compatible string would cause
all kinds of compatibility issues, both with older and newer DTs.

To avoid problems with newer kernels and older or newer DTs, we can change
the driver code to deduce the number of PHY instances from what's
described in the DT. This has the added advantage of not requiring new
compatible strings for new SoCs when just the number of PHYs change, which
already happened and might occur again in the future.

Drop the num_phys member from the config struct, and remove the fixed
number of PHYs from each SoC's config description. Then enumerate the
usb<x>_reset properties for all of the maximum four PHY instances, and
just stop once we cannot find such a property anymore.
The binding describes the reset property as mandatory for each PHY
instance, and each DT in the kernel tree matches exactly the num_phys
value in the current driver code, so we can rely on that.

Apart from being more future proof, this will solve the A523 mishap:
Older DTs would just describe two PHYs, whereas newer ones would feature
all three of them. In any case we would get a valid number, matching the
other nodes in the DT. Older kernels would always enumerate two PHYs,
which at least does not cause any regressions.

Signed-off-by: Andre Przywara <andre.przywara@arm.com>
Link: https://lore.kernel.org/r/20250819001522.13011-1-andre.przywara@arm.com
Signed-off-by: Vinod Koul <vkoul@kernel.org>

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