Decouple default features from esp-hal-common

[bugadani]

There are more assumptions in this PR than I'd like but the point is the same: esp-wifi will no longer enable default features. To prevent depending on esp-hal-common, I'm introducing a new feature in place of esp-hal-common/rv-zero-rtc-bss to clear up esp-wifi examples.

cc esp-rs/esp-wifi-sys#303 that uncovered the need for this.

[jessebraham]

Does it really make sense to add the esp-idf-boot feature if we're planning on removing the direct-boot feature? What do we actually gain from this?

[bugadani]

The feature name doesn't matter much, but there's also mcu-boot for a third option :) The end goal is to just have a feature in each hal crate that users can use instead of adding a mostly unnecessary dependency to the common crate.

As to my motivation: There are some users who need default-features = false to enable the 26 MHz crytal option.

PS: I do admit I don't actually know exactly when rv-zero-rtc-bs is necessary and where it isn't. It's also unclear to me if direct boot will be removed or not, there seem to be some people using it for one reason or another.

[jessebraham]

It's also unclear to me if direct boot will be removed or not, there seem to be some people using it for one reason or another.

We've had an RFC and have mentioned it in the last two community meetings and there has been basically zero feedback. As of now the plan is to remove it.

[bugadani]

I could just enable rv-zero-rtc-bs on esp-hal-common (same as features = ["esp32c3"] e.g.) and not add any new features, I just don't know if there are some cases where someone would want to have it disabled. At any rate, this is a draft for a reason, I'd love to hear opinions.

[bjoernQ]

It's also unclear to me if direct boot will be removed or not, there seem to be some people using it for one reason or another.

We've had an RFC and have mentioned it in the last two community meetings and there has been basically zero feedback. As of now the plan is to remove it.

At some point we probably need a decision since it's also broken for some targets (at least ESP32-S3). On the other hand, someone got esp-wifi working with direct-boot on ESP32-C3 ... that makes it a lot more useful now

[bjoernQ]

I guess it's fine to make the features individually available.
I don't think most users would need that granularity, however

[jessebraham]

I think after a rebase this is probably fine to merge.

[jessebraham]

LGTM, thanks!