Enable cpuidle support on i.MX6DL starting from IMX_CHIP_REVISION_1_1.

This also makes the code cleaner because 6q and 6dl actually have
different revision histories.
Signed-off-by: Bai Ping <ping.bai@nxp.com>
Signed-off-by: Leonard Crestez <leonard.crestez@nxp.com>
Reviewed-by: Lucas Stach <l.stach@pengutronix.de>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>