arm: Handle thumb2 thread entry point.

In cpu_set_upcall(), if the thread startup routine is a thumb routine, make
sure to set PSR_T, so that the CPU will run in thumb mode.

MFC After:      1 week

sys/arm/arm/vm_machdep.c

@@ -235,6 +235,8 @@ cpu_set_upcall(struct thread *td, void (*entry)(void *), void *arg,
 	tf->tf_pc = (int)entry;
 	tf->tf_r0 = (int)arg;
 	tf->tf_spsr = PSR_USR32_MODE;
+	if ((register_t)entry & 1)
+		tf->tf_spsr |= PSR_T;
 }
 
 int