Re-enable RE variant build for SKR Mini E3 1.2 boards.

[Floppy]

Description

Some SKR Mini E3 v1.2 boards have 512k of available memory, not 256k, and need the RE build to make use of it.

Requirements

BigTreeTech SKR Mini E3 v1.2 (sub-variant with a secret 512k of memory)

Benefits

Re-enables support for these variant boards, which many of us have been using happily for over a year.

Related Issues

• Remove BTT SKR Mini 512K "RCT6" Environments #22050 for discussion and testing
• Support 512K "RCT6" in BTT SKR Mini #15890 for the original discussion of 1.2 RET6 boards

[Floppy]

@Taomyn @rhapsodyv I know you folks have the same boards, if you could test this specific PR, I'm sure that would be helpful in getting this re-enabled in the official releass.

[Taomyn]

Works for me

[thisiskeithb]

This was removed on purpose.

If it works for your board, feel free to enable it in your fork, but it was not safe for everyone, and that is why the fake 512k envs were removed.

[Floppy]

@thisiskeithb that makes sense, for sure. Would adding a separate motherboard name like BTT_SKR_MINI_E3_V1_2_RET6 be more acceptable, or would you not want this capability in core at all?

Either way, this PR can act as a single-commit reference for people wanting to make the same change in future 👍

[thisiskeithb]

Would adding a separate motherboard name like BTT_SKR_MINI_E3_V1_2_RET6 be more acceptable, or would you not want this capability in core at all?

The 1.2 didn’t ship with an RET6, so adding a new fake board or environment is just bypassing the safety aspect and reason why the fake 512k envs were removed.

Again, feel free to overflash your board if it works for you, but those envs were removed for a reason.