Thank you all I have used the linked procedure - http://www.asyncro.com/2014/03/24/macbook-pro-discreate-graphics-card-issue-fix-updated/
Although while rebuilding the drivers cache it has given me down the line "segmentation fault" but when it booted:
I have noticed in Energy Saver "Automatic switching check box was removed now".Also My external video 6770m card is completely disabled as to test I have tried the game which previously was always going to 2nd gpu but now only using integrated GPU.
Also before doing all this I have updated to Yosemite.
Benefit of upgrade was :
Now when the system panics- Apple has made some changes in 6770m gpu drivers that is forcing the CPU to reinitialize or reboot the GPU - so now when system reboots it comes back safely. So no more recovery mode boot or single user or pram resets or SMC. It was coming back everytime.
But the disadvantage was everytime it was switching gpu during normal use it was crashing the laptop and rebooting. I had previously noticed the Webex Application infact was switching to external gpu and thus causing the system to hung[Maverik] or now reboot in Yosemite.
But now atleast its not anymore doing this, once I have disabled the 2nd GPU. So atleast, now I can use its internal card completely and its not a $3500/- paperweight.
Also we do not need gfxcardstatus app once we disable the external card.
Best of luck guys.