arm: a37xx: pci: Do not try to access other buses when link is down

arm: a37xx: pci: Do not try to access other buses when link is down

If a PIO request is executed while link-down, the whole controller gets
stuck in a non-functional state, and even after link comes up again, PIO
requests won't work anymore, and a reset of the whole PCIe controller is
needed. Therefore we need to prevent sending PIO requests while the link
is down.

Signed-off-by: Pali Rohár <pali@kernel.org>
Reviewed-by: Stefan Roese <sr@denx.de>