x86, hyperv: Fix build error due to missing <asm/apic.h> include

9e7827b5ea4c ("x86, hyperv: Get the local APIC timer frequency from the
hypervisor") breaks the build with some configs because apic.h isn't
directly included:

arch/x86/kernel/cpu/mshyperv.c: In function 'ms_hyperv_init_platform':
arch/x86/kernel/cpu/mshyperv.c:90:3: error: 'lapic_timer_frequency' undeclared (first use in this function)
arch/x86/kernel/cpu/mshyperv.c:90:3: note: each undeclared identifier is reported only once for each function it appears in

Fix it by including asm/apic.h.

Signed-off-by: David Rientjes <rientjes@google.com>
Link: http://lkml.kernel.org/r/alpine.DEB.2.02.1310111604160.31170@chino.kir.corp.google.com
Acked-by: K. Y. Srinivasan <kys@microsoft.com>
Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>

arch/x86/kernel/cpu/mshyperv.c

@@ -25,6 +25,7 @@
 #include <asm/idle.h>
 #include <asm/irq_regs.h>
 #include <asm/i8259.h>
+#include <asm/apic.h>
 
 struct ms_hyperv_info ms_hyperv;
 EXPORT_SYMBOL_GPL(ms_hyperv);