dt-bindings: phy: add binding document for Allwinner F1C100s USB PHY

Allwinner F1C100s has the most simple USB PHY among all Allwinner SoCs,
because it has only one OTG USB controller, no host-only OHCI/EHCI
controllers.

Add a binding document for it. Following the current situation of one
YAML file per SoC, this one is based on
allwinner,sun8i-v3s-usb-phy.yaml, but with OHCI/EHCI-related bits
removed. (The same driver in Linux, phy-sun4i-usb, covers all these
binding files now.)

Signed-off-by: Icenowy Zheng <uwu@icenowy.me>
Reviewed-by: Rob Herring <robh@kernel.org>
Reviewed-by: Andre Przywara <andre.przywara@arm.com>
Reviewed-by: Samuel Holland <samuel@sholland.org>
Signed-off-by: Andre Przywara <andre.przywara@arm.com>
Link: https://lore.kernel.org/r/20230109012223.4079299-2-andre.przywara@arm.com
Signed-off-by: Vinod Koul <vkoul@kernel.org>