[HVM] Support multiple HVM time device models coming soon.

[HVM] Support multiple HVM time device models coming soon.
        1: Adopt an abstract layer for periodic time on top of different
HV time device models like PIT, RTC and ACPI time.
        2: Extract VMM knowledge from PIT DM code and keep close with
qemu for easy maintain in future.
        3: Use guest time (TSC) to drive PIT CLK that helps us to remove
a lot of extra logic previously introduced to convert from host time to
guest time.
        4: Some cleanup for SMP code like move cache_tsc_offset to per VP.

Signed-off-by: Eddie Dong <eddie.dong@intel.com>