ARM: i.MX8M: Add DDR controller support ...

This adds the DDR driver for the i.MX8MQ/i.MX8MM. It's taken from
U-Boot v2020.04-rc1 with slight modifications for barebox

The i.MX8MQ boards in the tree currently use the output of an earlier
version of the NXP i.MX8M DDR Tool which doesn't use a controller driver
but instead does most stuff in board code. It seems this can coexist
with the new driver, only a few helper functions that previously lived
in arch/arm/mach-imx/imx8-ddrc.c are now provided by the new driver.

Tested on an i.MX8MM EVK

Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>

ddr: fsl: Add Freescale ddr driver ...

This adds the Freescale ddr driver used on various PowerPC and
Layerscape SoCs. This is based on U-Boot-2019.01 but with many
adjustments:

- PowerPC support has been removed
- CPP #ifdeffery replaced with C
- No more global variables/functions expected from the driver,
  configuration is passed by the board code which calls the driver

We already have the driver in the tree in an older version forked from
U-Boot-2013.04. This version lacks Layerscape support and many quirks
in the driver are PowerPC specific. Since the existing driver should
work on all known PowerPC and PowerPC is a dead end I decided not to
improve the existing driver and instead add a new Layerscape specific
driver.

Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>