Add zephyr github workflow

[quic-seaswara]

Add zephyr workflow, to build with LLVM and eld.

This would require building Zephyr and running tests for the following targets

• arm
• aarch64
• riscv32
• riscv64
• x86_64 (experimental)

You can also refer to zephyrproject-rtos/sdk-ng#777 for any additional information