usb: Move USB_UHCI_BIG_ENDIAN_* out of USB_SUPPORT

Move the Kconfig symbols USB_UHCI_BIG_ENDIAN_MMIO and
USB_UHCI_BIG_ENDIAN_DESC out of drivers/usb/host/Kconfig, which is
conditional upon USB && USB_SUPPORT, so that it can be freely selected
by platform Kconfig symbols in architecture code.

For example once the MIPS_GENERIC platform selects are fixed in commit
2e6522c5 ("MIPS: Fix typo BIG_ENDIAN to CPU_BIG_ENDIAN"), the MIPS
32r6_defconfig warns like so:

warning: (MIPS_GENERIC) selects USB_UHCI_BIG_ENDIAN_MMIO which has unmet direct dependencies (USB_SUPPORT && USB)
warning: (MIPS_GENERIC) selects USB_UHCI_BIG_ENDIAN_DESC which has unmet direct dependencies (USB_SUPPORT && USB)

Fixes: 2e6522c5

 ("MIPS: Fix typo BIG_ENDIAN to CPU_BIG_ENDIAN")
Signed-off-by: James Hogan <jhogan@kernel.org>
Cc: Corentin Labbe <clabbe.montjoie@gmail.com>
Cc: Ralf Baechle <ralf@linux-mips.org>
Cc: Paul Burton <paul.burton@mips.com>
Cc: linux-usb@vger.kernel.org
Cc: linux-mips@linux-mips.org
Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Patchwork: https://patchwork.linux-mips.org/patch/18559/