mshv: Use typed hv_stats_page pointers

mshv: Use typed hv_stats_page pointers

Refactor all relevant functions to use struct hv_stats_page pointers
instead of void pointers for stats page mapping and unmapping thus
improving type safety and code clarity across the Hyper-V stats mapping
APIs.

Signed-off-by: Stanislav Kinsburskii <skinsburskii@linux.microsoft.com>
Signed-off-by: Nuno Das Neves <nunodasneves@linux.microsoft.com>
Acked-by: Stanislav Kinsburskii <skinsburskii@linux.microsoft.com>
Reviewed-by: Michael Kelley <mhklinux@outlook.com>
Signed-off-by: Wei Liu <wei.liu@kernel.org>