pci: pcie-rcar-gen4: Assure reset occurs before DBI access

pci: pcie-rcar-gen4: Assure reset occurs before DBI access

Assure the reset is latched and the core is ready for DBI access.
On R-Car V4H, the PCIe reset is asynchronized and does not take
effect immediately, but needs a short time to complete. In case
DBI access happens in that short time, that access generates an
SError. Make sure that condition can never happen, read back the
state of the reset which should turn the asynchronized reset into
synchronized one, and wait a little over 1ms to add additional
safety margin.

Signed-off-by: Marek Vasut <marek.vasut+renesas@mailbox.org>