x86/xen: Move pv irq related functions under CONFIG_XEN_PV umbrella

All functions in arch/x86/xen/irq.c and arch/x86/xen/xen-asm*.S are
specific to PV guests. Include them in the kernel with CONFIG_XEN_PV only.

Make the PV specific code in arch/x86/entry/entry_*.S dependent on
CONFIG_XEN_PV instead of CONFIG_XEN.

The HVM specific code should depend on CONFIG_XEN_PVHVM.

While at it reformat the Makefile to make it more readable.

Signed-off-by: Juergen Gross <jgross@suse.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Acked-by: Thomas Gleixner <tglx@linutronix.de>
Cc: xen-devel@lists.xenproject.org
Cc: virtualization@lists.linux-foundation.org
Cc: akataria@vmware.com
Cc: rusty@rustcorp.com.au
Cc: hpa@zytor.com
Link: https://lkml.kernel.org/r/20180828074026.820-2-jgross@suse.com

diff --git a/include/xen/events.h b/include/xen/events.h
index c3e6bc6..a488971 100644
--- a/include/xen/events.h
+++ b/include/xen/events.h
@@ -89,11 +89,13 @@ unsigned irq_from_evtchn(unsigned int evtchn);
 int irq_from_virq(unsigned int cpu, unsigned int virq);
 unsigned int evtchn_from_irq(unsigned irq);
 
+#ifdef CONFIG_XEN_PVHVM
 /* Xen HVM evtchn vector callback */
 void xen_hvm_callback_vector(void);
 #ifdef CONFIG_TRACING
 #define trace_xen_hvm_callback_vector xen_hvm_callback_vector
 #endif
+#endif
 int xen_set_callback_via(uint64_t via);
 void xen_evtchn_do_upcall(struct pt_regs *regs);
 void xen_hvm_evtchn_do_upcall(void);