kvm tools: Fix reported RTC century and year

kvm tools: Fix reported RTC century and year

Commit 13d5097 ("kvm tools: Fix reported year in RTC emulation)
attempted to fix wrongly reported RTC year. However, as pointed out by
hpa the proper way to deal with this is to support the RTC century
field.

Suggested-by: H. Peter Anvin <hpa@zytor.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Ron Minnich <rminnich@gmail.com>
Cc: Asias He <asias.hejun@gmail.com>
Cc: Cyrill Gorcunov <gorcunov@openvz.org>
Cc: Sasha Levin <levinsasha928@gmail.com>
Signed-off-by: Pekka Enberg <penberg@kernel.org>