hvf: gate ARM_FEATURE_PMU register emulation when using the Apple vGIC

From Apple documentation: > When EL2 is disabled, PMU register accesses trigger "Trapped MSR, MRS, or > System Instruction" exceptions. When this happens, hv_vcpu_run() returns, and the >  hv_vcpu_exit_t object contains the information about this exception. > When EL2 is enabled, the handling of PMU register accesses is determined by the PMUVer > field of ID_AA64DFR0_EL1 register. > If the PMUVer field value is zero or is invalid, PMU register accesses generate "Undefined" > exceptions, which are sent to the guest. > If the PMUVer field value is non-zero and valid, PMU register accesses are emulated by the framework. > The ID_AA64DFR0_EL1 register can be modified via hv_vcpu_set_sys_reg API. However, despite what that documentation says this is actually gated on using the Apple vGIC instead of nested virtualisation per se. Apple introduced both at the same time. Signed-off-by: Mohamed Mediouni <mohamed@unpredictable.fr> Reviewed-by: Manos Pitsidianakis <manos.pitsidianakis@linaro.org> Message-id: 20260429190532.26538-8-mohamed@unpredictable.fr Signed-off-by: Peter Maydell <peter.maydell@linaro.org>