ENGR00315894-55 iMX6SX: add debug monitor support

ENGR00315894-55 iMX6SX: add debug monitor support

Debug monitor will print out last failed AXI access info when
system reboot is caused by AXI access failure, only works when
debug monitor is enabled.

Enable this module on i.MX6SX.

Signed-off-by: Anson Huang <b20788@freescale.com>
Signed-off-by: Ye.Li <B37916@freescale.com>
(cherry picked from commit df6ac8531d498021ed379c74fc1847bd2cec7179)
Signed-off-by: Peng Fan <Peng.Fan@freescale.com>
(cherry picked from commit 4f4ecdbf6fe2673b8ad117df1a4974bdb7e6aa4a)
(cherry picked from commit e1c98a672e50fd0405686b74dad50680a75a8a9f)
(cherry picked from commit 5265a3052505fae2a212af292412a62b20a16f97)