ARM: Implement a generic bios that use specific board code based on DTB

[tdecroyere]

ARM embedded devices like RPI 2b don't provide a machine layer abstraction like OpenSbi on RISC-V.

A generic bios needs to be implemented with specific implementation for each boards. The implementation will be selected at runtime based on DTB parsing.

This will allows to compile just for the CPU and not for each boards.

• Add the generic bios implementation for ARM.
• Implement a switch mechanism that can select the correct implementation based on the board info of DTB.
• Implement a basic version for RPI2B.
• Create a release workflow for RPI2B.