virtio-mem: check against mhp_get_pluggable_range() which memory we can hotplug

Right now, we only check against MAX_PHYSMEM_BITS - but turns out there
are more restrictions of which memory we can actually hotplug, especially
om arm64 or s390x once we support them: we might receive something like
-E2BIG or -ERANGE from add_memory_driver_managed(), stopping device
operation.

So, check right when initializing the device which memory we can add,
warning the user.  Try only adding actually pluggable ranges: in the worst
case, no memory provided by our device is pluggable.

In the usual case, we expect all device memory to be pluggable, and in
corner cases only some memory at the end of the device-managed memory
region to not be pluggable.

Link: https://lkml.kernel.org/r/1612149902-7867-5-git-send-email-anshuman.khandual@arm.com
Signed-off-by: David Hildenbrand <david@redhat.com>
Signed-off-by: Anshuman Khandual <anshuman.khandual@arm.com>
Cc: "Michael S. Tsirkin" <mst@redhat.com>
Cc: Jason Wang <jasowang@redhat.com>
Cc: Pankaj Gupta <pankaj.gupta.linux@gmail.com>
Cc: Oscar Salvador <osalvador@suse.de>
Cc: Wei Yang <richard.weiyang@linux.alibaba.com>
Cc: teawater <teawaterz@linux.alibaba.com>
Cc: Anshuman Khandual <anshuman.khandual@arm.com>
Cc: Pankaj Gupta <pankaj.gupta@cloud.ionos.com>
Cc: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Cc: Vasily Gorbik <gor@linux.ibm.com>
Cc: Will Deacon <will@kernel.org>
Cc: Ard Biesheuvel <ardb@kernel.org>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Heiko Carstens <hca@linux.ibm.com>
Cc: Michal Hocko <mhocko@kernel.org>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

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