xtensa: virt: fix PCI IO ports mapping

virt device tree incorrectly uses 0xf0000000 on both sides of PCI IO
ports address space mapping. This results in incorrect port address
assignment in PCI IO BARs and subsequent crash on attempt to access
them. Use 0 as base address in PCI IO ports address space.

Signed-off-by: Max Filippov <jcmvbkbc@gmail.com>