Modify default ddr config handling

[arikimari]

Summary

Remove default ddr configuration. Add function to return ddr configuration

Impact

Testing

[jlaitine]

I'd suggest not adding the CONFIG flag here; it is a bit confusing since some configuration is always needed.

Instead, in nuttx / imx9_ddr_training.c, make a "struct dram_timing_info * weak_function imx9_ddr_config()", returning a pointer to the default structure and call it directly in the beginning of "imx9_dram_init" to initialize the "ptiming" variable there.

Then we (or any board) can simply add an own version of the imx9_ddr_config(), which returns a pointer to our own structure.

[jlaitine]

This is fine, but perhaps add also the evk settings to the evk board with the same commit?

i.e.: The following should work

export PATH=$PATH:<path to compiler>
cd <path to nuttx>
./tools/configure.sh imx93-evk:bootloader
make

With this it would fail for the target, because there is no imx9_ddr_config function defined for the plain nuttx board.

When the imx9_ddr_config is also defined for the nuttx board, this commit can be upstreamed as well.

Also, please update the commit message (there is no longer the CONFIG_IMX9_DDR_CONFIG flag). Commit message should just describe that the default configuration is removed and ddr configuration is added to board instead.

[arikimari]

imx93 EVK does not have CONFIG_IMX9_DDR_TRAINING set so there is no need for imx9_ddr_config

[jlaitine]

imx93-evk:bootloader configuration has it, it doesn't link with this commit, just try it.

[jlaitine]

Looks good, let's just fix the commit title&message and the style check error (missing blank line).