PCI: dwc: Ensure FAST_LINK_MODE is cleared

PCI: dwc: Ensure FAST_LINK_MODE is cleared

"Fast Link Mode" is a simulation environment speed up setting which should
never be set and the default is not set. However some Amlogic platforms
have it set (by firmware presumably). See commit cdb8817395aa ("PCI:
amlogic: meson: Don't use FAST_LINK_MODE to set up link") for more
information. Let's clear it in core DWC code so we can drop some vendor
specific code.

Link: https://lore.kernel.org/r/20200821035420.380495-25-robh@kernel.org
Signed-off-by: Rob Herring <robh@kernel.org>
Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Cc: Jingoo Han <jingoohan1@gmail.com>
Cc: Gustavo Pimentel <gustavo.pimentel@synopsys.com>
Cc: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Cc: Bjorn Helgaas <bhelgaas@google.com>