phy: freescale: imx8m-pcie: Refine register definitions

No function changes, refine PHY register definitions.
- Keep align with other CMN PHY registers, refine the definitions of
  PHY_CMN_REG75.
- Remove two BIT definitions that are not used at all.

Signed-off-by: Richard Zhu <hongxing.zhu@nxp.com>
Signed-off-by: Lucas Stach <l.stach@pengutronix.de>
Tested-by: Marek Vasut <marex@denx.de>
Tested-by: Richard Leitner <richard.leitner@skidata.com>
Tested-by: Alexander Stein <alexander.stein@ew.tq-group.com>
Reviewed-by: Lucas Stach <l.stach@pengutronix.de>
Link: https://lore.kernel.org/r/1665625622-20551-3-git-send-email-hongxing.zhu@nxp.com
Signed-off-by: Vinod Koul <vkoul@kernel.org>