KVM: x86: hyper-v: Calculate APIC bus frequency for Hyper-V

Remove APIC_BUS_FREQUENCY and calculate it based on nanoseconds per APIC
bus cycle.  APIC_BUS_FREQUENCY is used only for HV_X64_MSR_APIC_FREQUENCY.
The MSR is not frequently read, calculate it every time.

There are two constants related to the APIC bus frequency:
APIC_BUS_FREQUENCY and APIC_BUS_CYCLE_NS.
Only one value is required because one can be calculated from the other:
   APIC_BUS_CYCLES_NS = 1000 * 1000 * 1000 / APIC_BUS_FREQUENCY.

Remove APIC_BUS_FREQUENCY and instead calculate it when needed.
This prepares for support of configurable APIC bus frequency by
requiring to change only a single variable.

Suggested-by: Maxim Levitsky <[email protected]>
Signed-off-by: Isaku Yamahata <[email protected]>
Reviewed-by: Maxim Levitsky <[email protected]>
Reviewed-by: Xiaoyao Li <[email protected]>
Reviewed-by: Rick Edgecombe <[email protected]>
[reinette: rework changelog]
Signed-off-by: Reinette Chatre <[email protected]>
Link: https://lore.kernel.org/r/76a659d0898e87ebd73ee7c922f984a87a6ab370.1714081726.git.reinette.chatre@intel.com
Signed-off-by: Sean Christopherson <[email protected]>

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