arm64: KVM: Add access handler for PMCNTENSET and PMCNTENCLR register

Since the reset value of PMCNTENSET and PMCNTENCLR is UNKNOWN, use
reset_unknown for its reset handler. Add a handler to emulate writing
PMCNTENSET or PMCNTENCLR register.

When writing to PMCNTENSET, call perf_event_enable to enable the perf
event. When writing to PMCNTENCLR, call perf_event_disable to disable
the perf event.

Signed-off-by: Shannon Zhao <shannon.zhao@linaro.org>
Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>

arch/arm64/include/asm/kvm_host.h

@@ -123,6 +123,7 @@ enum vcpu_sysreg {
 	PMEVCNTR0_EL0,	/* Event Counter Register (0-30) */
 	PMEVCNTR30_EL0 = PMEVCNTR0_EL0 + 30,
 	PMCCNTR_EL0,	/* Cycle Counter Register */
+	PMCNTENSET_EL0,	/* Count Enable Set Register */
 
 	/* 32bit specific registers. Keep them at the end of the range */
 	DACR32_EL2,	/* Domain Access Control Register */