x86/HVM: slightly adjust RTC reset

We should clear the interrupt enable flags here, deassert the IRQ, and
clear REG_C.

Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>

--- a/xen/arch/x86/hvm/rtc.c
+++ b/xen/arch/x86/hvm/rtc.c
@@ -732,6 +732,11 @@ void rtc_reset(struct domain *d)
     destroy_periodic_time(&s->pt);
     s->pt_code = 0;
     s->pt.source = PTSRC_isa;
+
+    s->hw.cmos_data[RTC_REG_B] &= ~(RTC_PIE | RTC_AIE | RTC_UIE);
+    if ( s->hw.cmos_data[RTC_REG_C] & RTC_IRQF )
+        hvm_isa_irq_deassert(d, RTC_IRQ);
+    s->hw.cmos_data[RTC_REG_C] = 0;
 }
 
 void rtc_init(struct domain *d)