target: arm: disassembler: fix Thumb2 BLX decoding address

Since BLX in Thumb2 always switches mode to ARM, the PC needs to be
4-bytes aligned.

Change-Id: I4f4c194fe21093cecfd9872e1d30588f4adc7257
Signed-off-by: Paul Fertser <fercerpav@gmail.com>
Reviewed-on: http://openocd.zylin.com/4382
Reviewed-by: Philipp Guehring <pg@futureware.at>
Tested-by: jenkins
Reviewed-by: Paul Sokolovsky <pfalcon@users.sourceforge.net>

src/target/arm_disassembler.c

@@ -2978,6 +2978,7 @@ static int t2ev_b_bl(uint32_t opcode, uint32_t address,
 	case 0x4:
 		inst = "BLX";
 		instruction->type = ARM_BLX;
+		address &= 0xfffffffc;
 		break;
 	case 0x5:
 		inst = "BL";