KVM: Move kvm_rebooting declaration out of x86

The variable kvm_rebooting is a common kvm variable, so move its
declaration from arch/x86/include/asm/kvm_host.h to
include/asm/kvm_host.h.

Fixes this sparse warning when building on arm64:

  virt/kvm/kvm_main.c⚠️ symbol 'kvm_rebooting' was not declared. Should it be static?

Signed-off-by: Geoff Levand <geoff@infradead.org>
Signed-off-by: Gleb Natapov <gleb@redhat.com>

arch/x86/include/asm/kvm_host.h

@@ -972,7 +972,6 @@ enum {
  * Trap the fault and ignore the instruction if that happens.
  */
 asmlinkage void kvm_spurious_fault(void);
-extern bool kvm_rebooting;
 
 #define ____kvm_handle_fault_on_reboot(insn, cleanup_insn)	\
 	"666: " insn "\n\t" \

include/linux/kvm_host.h

@@ -1061,6 +1061,8 @@ static inline bool kvm_check_request(int req, struct kvm_vcpu *vcpu)
 	}
 }
 
+extern bool kvm_rebooting;
+
 #ifdef CONFIG_HAVE_KVM_CPU_RELAX_INTERCEPT
 
 static inline void kvm_vcpu_set_in_spin_loop(struct kvm_vcpu *vcpu, bool val)