Hi. After playing with lcd on Android, I realised that the backlight polarity was opposite. When I changed the setting of brightness to max on android the backlight was off completely. To reverse this I had to change the fex file. I changed lcd_pwm_pol from 0 to 1.
Also there is a flashing when you make screen on and off by clicking power button. After looking at tablet designs I saw that lcd_bl_en wasn't used in A13-Olinuxino. I think that might have solved this issue. But this is a minor issue. Other than that everything works just fine now.
It can be solved changing lcd_pwm_pol from 0 to 1 in script.fex