target/arm/hvf: Mention hvf_arch_set_traps() must run on vCPU thread

Since hvf_arch_set_traps() calls hv_vcpu_set_trap_debug_exceptions()
and hv_vcpu_set_trap_debug_reg_accesses(), which must run on a vCPU,
it also must. Mention it.

Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Reviewed-by: Mads Ynddal <mads@ynddal.dk>
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>

target/arm/hvf/hvf.c

@@ -2192,6 +2192,7 @@ static inline bool hvf_arm_hw_debug_active(CPUState *cpu)
     return ((cur_hw_wps > 0) || (cur_hw_bps > 0));
 }
 
+/* Must be called by the owning thread */
 static void hvf_arch_set_traps(CPUState *cpu)
 {
     bool should_enable_traps = false;