Add support for booting a bzImage Linux Kernel

[conradgrobler]

Stage 0 can now boot either an uncompressed 64-bit ELF kernel, or a 64-bit compressed Linux kernel using the bzImage format.

To boot using an ELF kernel, use the custom file paths in QEMU, e.g:

qemu-system-x86_64 -cpu host -enable-kvm -machine "microvm,acpi=on" -m 1G \
  -nographic -nodefaults -no-reboot -serial stdio -bios "bin/stage0.bin" \
  -fw_cfg "name=opt/stage0/elf_kernel,file=bin/vmlinux" \
  -fw_cfg "name=opt/stage0/initramfs,file=bin/initramfs" \
  -fw_cfg "name=opt/stage0/cmdline,string=console=ttyS0 quiet"

To boot using a bzImage kernel, use the normal QEMU direct-booting paramters, e.g.

qemu-system-x86_64 -cpu host -enable-kvm -machine "microvm,acpi=on" -m 1G \
  -nographic -nodefaults -no-reboot -serial stdio -bios "bin/stage0.bin" \
  -append "console=ttyS0 quiet" -kernel "bin/bzImage" -initrd "bin/initramfs"

Removing support for parsing ELF kernels in Stage 0 will be done as a future cleanup.

[github-actions]

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[github-actions]

artifact_name = "oak_echo_raw_enclave_app"
artifact_digest = "sha256:39051983bbb600bbfb91bd22ee4c976420f8f0c6a895fd083dcb0d153ddd5fd6"
provenance_digest = "sha256:9d1d3d2cd428a42e15e54a0b60ca2178371504eeb3e852fbb6c6291b7646d32f"

[github-actions]

artifact_name = "stage0_bin"
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[github-actions]

artifact_name = "quirk_echo_enclave_app"
artifact_digest = "sha256:fe5047e49d03e8c41057fc2a05baa6a1721dcc0f94537a11b33ee9f83c7ebe63"
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[github-actions]

artifact_name = "oak_restricted_kernel_bin"
artifact_digest = "sha256:6d9377bc3a82c5925810192d6ac99197c39a3cd4c37dee8af2bcb3216214abf6"
provenance_digest = "sha256:92eb1a7dc979568269316a31164b2612477299a55160fc5901993d37033c6336"

[github-actions]

artifact_name = "oak_restricted_kernel_simple_io_bin"
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[github-actions]

artifact_name = "oak_functions_enclave_app"
artifact_digest = "sha256:22974c823e72cab5f6aa9ececf2509d8b96aae8a9eeb3f8c6c1e63be7ce35376"
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