KVM: X86: Rename kvm_compute_tsc_offset() to kvm_compute_l1_tsc_offset()

All existing code uses kvm_compute_tsc_offset() passing L1 TSC values to
it. Let's document this by renaming it to kvm_compute_l1_tsc_offset().

Signed-off-by: Ilias Stamatis <ilstam@amazon.com>
Reviewed-by: Maxim Levitsky <mlevitsk@redhat.com>
Message-Id: <20210526184418.28881-4-ilstam@amazon.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>