fix: Don't allow select MULTI_TRAINER if no MULTI

[pfeerick]

Fixes #1563 by ensuring Multi Trainer opt is not shown if no MPM
is enabled, as well as if MPM suport is not even compiled in.

It should only prevent TRAINER_MODE_MULTI being an selectable trainer mode if:

• MULTIMODULE support not enabled
• You don't have any modules enabled at all
• Neither of the enabled modules are MPM

It seems that having two MPMs enabled is a valid case, so I've left that case alone.

Hardware tested on TX16S and TX12-MK2, and working as expected.

For me, this is both a bug (letting you select something that you can't) and an enhancement (don't show me stuff I can't use)... 🤷 😆

[gagarinlg]

I can confirm that having two MPMs is a thing.
One for the connection to the model and one for the connection to the trainee radio

[pfeerick]

@HThuren What's the equiv. of "OFF" (i.e Off, but uppercase) for Danish?
#define TR_VTRAINER_MASTER_OFF "Fra"

@ulfhedlund The same here, but for Swedish...
#define TR_VTRAINER_MASTER_OFF "Av"

I'm wanting to restore a change that as made in #1806 that looks like it got overwritten as part of rebasing the LVGL code - where we standardised on all uppercase for "OFF" for when trainer mode was, well, OFF! But it's also ok if it is left as it is since yours is translated - but though I should check before just making it uppercase incase that changes meaning ;)

[HThuren]

Hi @pfeerick, I use OFF = "FRA" and Off = "Fra", when only the one word.
Thank you for asking :-)

[HThuren]

Notice #2301, where changes are made to #2294

[ulfhedlund]

Sorry I've missed this but I believe you already figured out it is AV for OFF in Swedish :)