virtio-balloon: Replace free page hinting references to 'report' with 'hint'

Recently a feature named Free Page Reporting was added to the virtio
balloon. In order to avoid any confusion we should drop the use of the word
'report' when referring to Free Page Hinting. So what this patch does is go
through and replace all instances of 'report' with 'hint" when we are
referring to free page hinting.

Acked-by: David Hildenbrand <david@redhat.com>
Signed-off-by: Alexander Duyck <alexander.h.duyck@linux.intel.com>
Message-Id: <20200720175128.21935.93927.stgit@localhost.localdomain>
Cc: qemu-stable@nongnu.org
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>