I get two way options to start lampp on boot time,

Option 1:

Open the rc.local file and add the line

# sudo gedit /etc/rc.local

/opt/lampp/lampp start

Option 2 :

Chkconfig to start lampp service during the system startup. Create a softlink  /opt/lampp/lampp /etc/init.d/lampp
# ln -s /opt/lampp/lampp /etc/init.d/lampp

Then, can run the below commands :
# service lampp start


#/etc/init.d/lampp start
Starting XAMPP for Linux 1.8.2-4...
XAMPP: Starting Apache...ok.
XAMPP: Starting MySQL...ok.
XAMPP: Starting ProFTPD...ok.

lampp to be added in chkconfig for service will start during the system startup
# chkconfig --levels 235 lampp on

To verify the chkconfig
# chkconfig --list | grep lampp
lampp           0:off   1:off   2:off   3:on    4:off   5:on    6:off