ddr: Add DDR driver for iMX8ULP

Add iMX8ULP DDR initialization driver which loads the DDR timing
parameters and executes the training procedure.

When enabling IMX8ULP_DRAM_PHY_PLL_BYPASS, using PHY PLL bypass mode
to do DDR init

Signed-off-by: Ye Li <ye.li@nxp.com>
diff --git a/drivers/ddr/imx/Kconfig b/drivers/ddr/imx/Kconfig
index 7e06fb2..179f345 100644
--- a/drivers/ddr/imx/Kconfig
+++ b/drivers/ddr/imx/Kconfig
@@ -1 +1,2 @@
 source "drivers/ddr/imx/imx8m/Kconfig"
+source "drivers/ddr/imx/imx8ulp/Kconfig"