x86/kexec: Drop page_list argument from relocate_kernel()

The kernel's virtual mapping of the relocate_kernel page currently needs
to be RWX because it is written to before the %cr3 switch.

Now that the relocate_kernel page has its own .data section and local
variables, it can also have *global* variables. So eliminate the separate
page_list argument, and write the same information directly to variables
in the relocate_kernel page instead. This way, the relocate_kernel code
itself doesn't need to copy it.

Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Cc: Baoquan He <bhe@redhat.com>
Cc: Vivek Goyal <vgoyal@redhat.com>
Cc: Dave Young <dyoung@redhat.com>
Cc: Eric Biederman <ebiederm@xmission.com>
Cc: Ard Biesheuvel <ardb@kernel.org>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Link: https://lore.kernel.org/r/20241205153343.3275139-11-dwmw2@infradead.org