x86/Kconfig: Add new X86_HV_CALLBACK_VECTOR config symbol

Add a special Kconfig symbol X86_HV_CALLBACK_VECTOR so that the guests
using the hypervisor interrupt callback counter can select and thus
enable that counter. Select it when xen or hyperv support is enabled. No
functional changes.

Signed-off-by: Zhao Yakui <yakui.zhao@intel.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Reviewed-by: Borislav Petkov <bp@suse.de>
Reviewed-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Cc: Frederic Weisbecker <frederic@kernel.org>
Cc: Haiyang Zhang <haiyangz@microsoft.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Juergen Gross <jgross@suse.com>
Cc: "K. Y. Srinivasan" <kys@microsoft.com>
Cc: linux-hyperv@vger.kernel.org
Cc: Nicolai Stange <nstange@suse.de>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Sasha Levin <sashal@kernel.org>
Cc: Stefano Stabellini <sstabellini@kernel.org>
Cc: Stephen Hemminger <sthemmin@microsoft.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: x86-ml <x86@kernel.org>
Cc: xen-devel@lists.xenproject.org
Link: https://lkml.kernel.org/r/1559108037-18813-2-git-send-email-yakui.zhao@intel.com