PCI: imx6: Do not wait for speed change on i.MX7

As can be seen from [1]:

  "...the different behavior between iMX6Q PCIe and iMX7D PCIe maybe caused
  by the different controller version.

  Regarding to the DOC description, the DIRECT_SPEED_CHANGE should be
  cleared after the speed change from GEN1 to GEN2. Unfortunately, when
  GEN1 device is used, the behavior is not documented.

  So, IC design guys run the simulation and find out the following
  behaviors:

     1. DIRECT_SPEED_CHANGE will be cleared in 7D after speed change
     	from GEN1 to GEN2. This matches doc’s description

     2. set MAX link speed(PCIE_CAP_TARGET_LINK_SPEED=0x01) as GEN1 and
     	re-run the simulation, DIRECT_SPEED_CHANGE will not be cleared;
     	remain as 1, this matches your result, but function test is
     	passed, so this bit should not affect the normal PCIe function."

imx6_pcie_wait_for_speed_change() will report false failures for Gen1 ->
Gen1 speed transition, so avoid doing that check and just rely on
imx6_pcie_wait_for_link() only.

[1] https://community.nxp.com/message/867943



Signed-off-by: Andrey Smirnov <andrew.smirnov@gmail.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Reviewed-by: Lucas Stach <l.stach@pengutronix.de>
Cc: yurovsky@gmail.com
Cc: Fabio Estevam <fabio.estevam@nxp.com>
Cc: Dong Aisheng <dongas86@gmail.com>
Cc: linux-arm-kernel@lists.infradead.org