PCI: dwc/imx6: Remove duplicate define PCIE_LINK_WIDTH_SPEED_CONTROL

PCI: dwc/imx6: Remove duplicate define PCIE_LINK_WIDTH_SPEED_CONTROL

PCIE_LINK_WIDTH_SPEED_CONTROL is already defined in pcie-designware.h,
so remove it from the i.MX6 driver.

Link: https://lore.kernel.org/r/20200821035420.380495-23-robh@kernel.org
Signed-off-by: Rob Herring <robh@kernel.org>
Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Cc: Richard Zhu <hongxing.zhu@nxp.com>
Cc: Lucas Stach <l.stach@pengutronix.de>
Cc: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Cc: Bjorn Helgaas <bhelgaas@google.com>
Cc: Shawn Guo <shawnguo@kernel.org>
Cc: Sascha Hauer <s.hauer@pengutronix.de>
Cc: Pengutronix Kernel Team <kernel@pengutronix.de>
Cc: Fabio Estevam <festevam@gmail.com>
Cc: NXP Linux Team <linux-imx@nxp.com>