imx: add support for i.MX7/i.MX8MQ reset controller

Add support for the reset controller that's used on the i.MX7D
and i.MX8MQ.  This will be needed to be able to assert the PCIe
reset pins.  Bindings taken from Linux, driver implementation
mostly taken from Linux and adjusted to U-Boot infrastructure.

Signed-off-by: Patrick Wildt <patrick@blueri.se>
Reviewed-by: Fabio Estevam <festevam@gmail.com>
diff --git a/drivers/reset/Makefile b/drivers/reset/Makefile
index 7fec75b..f5875fc 100644
--- a/drivers/reset/Makefile
+++ b/drivers/reset/Makefile
@@ -20,3 +20,4 @@
 obj-$(CONFIG_RESET_MEDIATEK) += reset-mediatek.o
 obj-$(CONFIG_RESET_SUNXI) += reset-sunxi.o
 obj-$(CONFIG_RESET_HISILICON) += reset-hisilicon.o
+obj-$(CONFIG_RESET_IMX7) += reset-imx7.o