kho: add support for preserving vmalloc allocations

kho: add support for preserving vmalloc allocations

A vmalloc allocation is preserved using binary structure similar to global
KHO memory tracker.  It's a linked list of pages where each page is an
array of physical address of pages in vmalloc area.

kho_preserve_vmalloc() hands out the physical address of the head page to
the caller.  This address is used as the argument to kho_vmalloc_restore()
to restore the mapping in the vmalloc address space and populate it with
the preserved pages.

[pasha.tatashin@soleen.com: free chunks using free_page() not kfree()]
Link: https://lkml.kernel.org/r/mafs0a52idbeg.fsf@kernel.org
[akpm@linux-foundation.org: coding-style cleanups]
Link: https://lkml.kernel.org/r/20250921054458.4043761-4-rppt@kernel.org
Signed-off-by: Mike Rapoport (Microsoft) <rppt@kernel.org>
Reviewed-by: Pratyush Yadav <pratyush@kernel.org>
Cc: Alexander Graf <graf@amazon.com>
Cc: Baoquan He <bhe@redhat.com>
Cc: Changyuan Lyu <changyuanl@google.com>
Cc: Chris Li <chrisl@kernel.org>
Cc: Jason Gunthorpe <jgg@nvidia.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>