KVM: x86: Move kvm_set_apic_base() implementation to lapic.c (from x86.c)

KVM: x86: Move kvm_set_apic_base() implementation to lapic.c (from x86.c)

Move kvm_set_apic_base() to lapic.c so that the bulk of KVM's local APIC
code resides in lapic.c, regardless of whether or not KVM is emulating the
local APIC in-kernel.  This will also allow making various helpers visible
only to lapic.c.

No functional change intended.

Reviewed-by: Kai Huang <kai.huang@intel.com>
Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>
Link: https://lore.kernel.org/r/20241009181742.1128779-6-seanjc@google.com
Link: https://lore.kernel.org/r/20241101183555.1794700-6-seanjc@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>