add arm_blx_label(_thumb) testcase

suite/regress/arm_blx_label.py

 #!/usr/bin/python
 
-# Test BL <label> instruction for ARM32
+# Test BLX <label> instruction for ARM32
 
 # Github issue: #248
 # Author: dmxcsnsbh

suite/regress/arm_blx_label_thumb.py

 #!/usr/bin/python
 
-# Test BL <label> instruction for ARM32
+# Test BLX <label> instruction for THUMB
 
 # Github issue: #248
 # Author: dmxcsnsbh