Multi SoC embedded runner

[daringer]

hey hey,

we wanted to share our current state of what we call the embedded runner, which introduces nRF52 support with an infrastructure capable of even more SoC implementations. LPC55 is also included (although not every detail was ported yet).

• based on the current solo2 upstream
• the init phase is now modularized with src/bin/app-nrf.rs and src/bin/app-lpc.rs representing the "entry-point"
• building is now driven by profiles/ to create essential build-constants.rs and memory.x during compile-time
• within embedded/src/ (excluding soc_* and bin/) all sources are generic for all SoCs (still some things might be pulled out from the specific SoC dirs)
• please ignore nrf-bootloader, this builds the nRF52 bootloader my feeling is this should not be there, although I also don't see where it should fit better, the bottom part of the Makefile is also therefore WIP
• deployment is essentially for dev/testing, so also please ignore

looking forward for your feedback how you think about this approach and if this might be something you would like to upstream at some point