Some SoC based on ipq8064/5 needs to be limited to pci GEN1 speed due to
some hardware limitations. Add support for speed setting defined by the
max-link-speed binding. If not defined the max speed is set to GEN2 by
default.

Link: https://lore.kernel.org/r/20200615210608.21469-12-ansuelsmth@gmail.comSigned-off-by: NSham Muthayyan <smuthayy@codeaurora.org>
Signed-off-by: NAnsuel Smith <ansuelsmth@gmail.com>
Signed-off-by: NLorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Reviewed-by: NRob Herring <robh@kernel.org>
Acked-by: NStanimir Varbanov <svarbanov@mm-sol.com>