- Add support to test available memory.
- Add test configuration for 2 GiB variant.
- Use BRD_REV0 and BRD_REV1 signals to detect memory variant of the
  module. Currently, 2 GiB and 4 GiB memory variants are supported.
Signed-off-by: Thomas Schaefer <thomas.schaefer@kontron.com>

- use the lpddr4_timing.c file generated by DDR stress test
  tool for board specific lpddr4 timing settings.
- use NXP LPDDR4 driver located in drivers/ddr/imx/imx8m by
  enabling the IMX8M_LPDDR4 configuration setting.
Signed-off-by: Thomas Schaefer <thomas.schaefer@kontron.com>

Signed-off-by: Thomas Schaefer <thomas.schaefer@kontron.com>