KVM: SVM: Do not setup frame pointer in __svm_vcpu_run

__svm_vcpu_run is a leaf function and does not need
a frame pointer.  %rbp is also destroyed a few instructions
later when guest registers are loaded.

Cc: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Uros Bizjak <ubizjak@gmail.com>
Message-Id: <20200409120440.1427215-1-ubizjak@gmail.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>