This is necessary for being able to use the qemu `-kernel` option.
The QEMU virt machine uses OpenSBI's FW_DYNAMIC feature to pass
the kernel entry address, which is the virtual entry point address
specified in the kernel ELF. If we instead `objcopy` the kernel into a
raw binary, OpenSBI will jump to the physical kernel load address, which
is what we want it to do.
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