x86/vmx: fix vmx_is_singlestep_supported return value

The function supposed to return a boolean but instead it returned
the value 0x8000000 which is the Intel internal flag for MTF. This has
caused various checks using this function to falsely report no MTF
capability.

Signed-off-by: Tamas K Lengyel <tlengyel@novetta.com>
Reviewed-by: Andrew Cooper <andrew.cooper3@citrix.com>
Acked-by: Kevin Tian <kevin.tian@intel.com>
Release-acked-by: Wei Liu <wei.liu2@citrix.com>

xen/arch/x86/hvm/vmx/vmx.c

@@ -1768,7 +1768,7 @@ static void vmx_enable_msr_exit_interception(struct domain *d)
 
 static bool_t vmx_is_singlestep_supported(void)
 {
-    return cpu_has_monitor_trap_flag;
+    return !!cpu_has_monitor_trap_flag;
 }
 
 static void vmx_vcpu_update_eptp(struct vcpu *v)