x86/hyperv: Make hv_get_nmi_reason public

Move hv_get_nmi_reason to .h file so it can be used in other
modules as well.

Signed-off-by: Saurabh Sengar <ssengar@linux.microsoft.com>
Reviewed-by: Michael Kelley <mikelley@microsoft.com>
Link: https://lore.kernel.org/r/1681192532-15460-4-git-send-email-ssengar@linux.microsoft.com


Signed-off-by: Wei Liu <wei.liu@kernel.org>