mm/memory_hotplug: rename all existing 'memhp' into 'mhp'

This renames all 'memhp' instances to 'mhp' except for memhp_default_state
for being a kernel command line option.  This is just a clean up and
should not cause a functional change.  Let's make it consistent rater than
mixing the two prefixes.  In preparation for more users of the 'mhp'
terminology.

Link: https://lkml.kernel.org/r/1611554093-27316-1-git-send-email-anshuman.khandual@arm.com


Signed-off-by: Anshuman Khandual <anshuman.khandual@arm.com>
Suggested-by: David Hildenbrand <david@redhat.com>
Reviewed-by: David Hildenbrand <david@redhat.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: "Rafael J. Wysocki" <rafael@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>