KVM: SVM,VMX: Use %rip-relative addressing to access kvm_rebooting

Instruction with %rip-relative address operand is one byte shorter than
its absolute address counterpart and is also compatible with position
independent executable (-fpie) build.

No functional changes intended.

Cc: Sean Christopherson <seanjc@google.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Uros Bizjak <ubizjak@gmail.com>
Link: https://lore.kernel.org/r/20231031075312.47525-1-ubizjak@gmail.com
Signed-off-by: Sean Christopherson <seanjc@google.com>