crashdump/x86: dump any kind of "System RAM"

Traditionally, we had "System RAM" only on the top level of in the
kernel resource tree (-> /proc/iomem). Nowadays, we can also have
"System RAM" on lower levels of the tree -- driver-managed device memory
that is always detected and added via drivers. Current examples are
memory added via dax/kmem -- ("System RAM (kmem)") and virtio-mem ("System
RAM (virtio_mem)"). Note that in some kernel versions "System RAM
(kmem)" was exposed as "System RAM", but similarly, on lower levels of
the resource tree.

Let's add anything that contains "System RAM" to the elf core header, so
it will be dumped for kexec_load(). Handling kexec_file_load() in the
kernel is similarly getting fixed [1].

Loading a kdump kernel via "kexec -p -c" ... will result in the kdump
kernel to also dump dax/kmem and virtio-mem added System RAM now.

Note: We only want to dump this memory, we don't want to add this memory to
the memmap of an ordinary kexec'ed kernel ("fast system reboot").

[1] https://lkml.kernel.org/r/20210322160200.19633-1-david@redhat.com

Signed-off-by: David Hildenbrand <david@redhat.com>
Acked-by: Dave Hansen <dave.hansen@linux.intel.com>
Signed-off-by: Simon Horman <horms@verge.net.au>

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