KVM: selftests: Add test for configure of x86 APIC bus frequency

KVM: selftests: Add test for configure of x86 APIC bus frequency

Test if KVM emulates the APIC bus clock at the expected frequency when
userspace configures the frequency via KVM_CAP_X86_APIC_BUS_CYCLES_NS.

Set APIC timer's initial count to the maximum value and busy wait for 100
msec (largely arbitrary) using the TSC. Read the APIC timer's "current
count" to calculate the actual APIC bus clock frequency based on TSC
frequency.

Suggested-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Isaku Yamahata <isaku.yamahata@intel.com>
Co-developed-by: Reinette Chatre <reinette.chatre@intel.com>
Signed-off-by: Reinette Chatre <reinette.chatre@intel.com>
Link: https://lore.kernel.org/r/2fccf35715b5ba8aec5e5708d86ad7015b8d74e6.1718214999.git.reinette.chatre@intel.com
Signed-off-by: Sean Christopherson <seanjc@google.com>