clocksource/drivers/hyperv: add data structure for reference TSC MSR

Add a data structure to represent the reference TSC MSR similar to
other MSRs. This simplifies the code for updating the MSR.

Signed-off-by: Anirudh Rayabharam <anrayabh@linux.microsoft.com>
Reviewed-by: Michael Kelley <mikelley@microsoft.com>
Link: https://lore.kernel.org/r/20221027095729.1676394-2-anrayabh@linux.microsoft.com
Signed-off-by: Wei Liu <wei.liu@kernel.org>