Improve cross-architecture builds

Currently building multi-arch images takes hours. Most of time is spend building OTP from source in full qemu emulation mode.

Instead of building from source using buildx try cross-compiling it similar to https://github.com/esl/packages/commit/204a126e4d4b94744089e75970b8f12d2686097a

Start by reviewing the buildx configuration and the OTP build path used for multi-architecture images, then compare it with the linked esl/packages cross-compilation commit. Done means the image build cross-compiles OTP instead of using full QEMU emulation and significantly reduces multi-architecture build time.

Written by the indexing model from the issue text.