Staging: hyperv: add clocksource driver

This patch is a clocksource implementation suitable for guests hosted on
HyperV.  Time keeping in Linux guests hosted on HyperV is unstable. This
clocksource driver fixes the problem. This driver uses the hyperv
detection code integrated into the kernel.

Signed-off-by: K. Y. Srinivasan <ksrinivasan@novell.com>
Cc: Hank Janssen <hjanssen@microsoft.com>
Cc: Haiyang Zhang <haiyangz@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>