{bp-16533} Update MCUBoot build process for Espressif devices

[jerpelea]

Summary

arch/risc-v: decouple common source for Espressif's MCUBoot port
Decouples the NuttX build from the MCUBoot common source on RISC-V Espressif
devices. Allows using different branches for each.

arch/xtensa: decouple common source for Espressif's MCUBoot port
Decouples the NuttX build from the MCUBoot common source on Xtensa
devices. Allows using different branches for each.

This PR changes MCUBoot build process for Xtensa and RISC-V Espressif devices. No changes on user side or build process.

Impact

RELEASE

Testing

CI