x86: tsc: add support for reading CPU freq from cpuid

Starting with cpuid level 0x16 (Skylake-based processors)
it is possible to get CPU base freq via cpuid.

This fixes booting on a skylake based system.

Signed-off-by: Christian Gmeiner <christian.gmeiner@gmail.com>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>
[bmeng: fixed wrong indention of labels]
Signed-off-by: Bin Meng <bmeng.cn@gmail.com>