ddr: fsl: depend on ARM ...

We have inline assembly in the driver, so we can't compile-test it
unmodified on non-ARM. Indicate so in the Kconfig.

Signed-off-by: Ahmad Fatoum <a.fatoum@pengutronix.de>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>

drivers: add COMPILE_TEST prompts for some off-by-default options ...

Some Kconfig options we have are promptless and off-by-default and
instead can only be enabled by being selected from platform options.

For some of those that aren't compile testable, add a new
COMPILE_TEST-only prompt.

Signed-off-by: Ahmad Fatoum <a.fatoum@pengutronix.de>
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>