pitx-imx8m: add memory variant support
- 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>