kernel: fix kmod-usb3 dependencies

kernel: fix kmod-usb3 dependencies

Adding CONFIG_USB_XHCI_PCI_RENESAS to KCONFIG made it so it was set
for all targets that included kmod-usb3, not just the intended
apm821xx/nand. xhci-pci has a dependency on xhci-pci-renesas if
CONFIG_USB_XHCI_PCI_RENESAS is set, breaking kmod-usb3 builds on
Linux 5.10 on all other targets.

Rework the dependencies by breaking out xhci-hcd, xhci-mtk, and
xhci-pci-renesas into new hidden kernel modules and setting kmod-usb3
dependencies properly.

Tested by building mt7621 and apm821xx/nand with kmod-usb3 on Linux 5.10

Fixes: be23f981 ("apm821xx: add support for kernel 5.10")
Cc: Christian Lamparter <chunkeey@gmail.com>
Signed-off-by: Ilya Lipnitskiy <ilya.lipnitskiy@gmail.com>