hw/core: Add Enclave Image Format (EIF) related helpers

hw/core: Add Enclave Image Format (EIF) related helpers

An EIF (Enclave Image Format)[1] file is used to boot an AWS nitro
enclave[2] virtual machine. The EIF file contains the necessary kernel,
cmdline, ramdisk(s) sections to boot.

Some helper functions have been introduced for extracting the necessary
sections from an EIF file and then writing them to temporary files as
well as computing SHA384 hashes from the section data. These will be
used in the following commit to add support for nitro-enclave machine
type in QEMU.

The files added in this commit are not compiled yet but will be added
to the hw/core/meson.build file in the following commit where
CONFIG_NITRO_ENCLAVE will be introduced.

[1] https://github.com/aws/aws-nitro-enclaves-image-format
[2] https://docs.aws.amazon.com/enclaves/latest/user/nitro-enclave.html

Signed-off-by: Dorjoy Chowdhury <dorjoychy111@gmail.com>
Reviewed-by: Alexander Graf <graf@amazon.com>
Link: https://lore.kernel.org/r/20241008211727.49088-4-dorjoychy111@gmail.com
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>