KVM: x86: Set BSP bit in reset BSP vCPU's APIC base by default

Set the BSP bit appropriately during local APIC "reset" instead of
relying on vendor code to clean up at a later point.  This is a step
towards consolidating the local APIC, VMX, and SVM xAPIC initialization
code.

Reviewed-by: Reiji Watanabe <reijiw@google.com>
Signed-off-by: Sean Christopherson <seanjc@google.com>
Message-Id: <20210713163324.627647-16-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>