Figure out cross-model resource (non)sharing

[matejcik]

For Model T we need FIDO icons and some other resources in color. For models 1 and R, we need them in black & white. It would be great to have a way of excluding resources from the build that won't be used in the result.

A possible way forward is to move the resources to Rust, where either linker or conditional compilation would take care of it.

(doing just resources.rs generated by Mako should be pretty easy, given that we now have obj_module! and can expose individual images as attributes essentially for free. The generator can take care of inclusion/exclusion via directories, so, say:

• resources/common/icon_gear.toif is included unconditionally
• resources/tt/homescreen.toif is included as #[cfg(feature = "model_tt")]

would be nice and hopefully not too difficult to teach obj_module! about features)

[mmilata]

We already do have some conditionally included resources in rust code: https://github.com/trezor/trezor-firmware/blob/core/v2.5.1/core/embed/rust/src/ui/model_tt/theme.rs#L45-L55