clocksource: hyper-v: Mark hyperv tsc page unencrypted in sev-snp enlightened guest

Hyper-V tsc page is shared with hypervisor and mark the page
unencrypted in sev-snp enlightened guest when it's used.

Reviewed-by: Dexuan Cui <decui@microsoft.com>
Reviewed-by: Michael Kelley <mikelley@microsoft.com>
Signed-off-by: Tianyu Lan <tiala@microsoft.com>
Signed-off-by: Wei Liu <wei.liu@kernel.org>
Link: https://lore.kernel.org/r/20230818102919.1318039-7-ltykernel@gmail.com