Macbook Pro 2011 : After disabling the dGPU using Arch, normal boot hang halfway but working in safe boot I have followed all the instructions provided at 
MacBook Pro: How to disable discrete GPU permanently from EFI? 
and I'm stuck at the following step:


  3.1 Move AMD / NVIDIA kext files to a backup directory
  
  Remove all the AMD (or NVIDIA, depending on your card) kext files in
  the Terminal in Recovery Console. Trying to remove them in Single User
  just gives sandbox errors, so don’t do it in Single User Mode! (the
  one that you boot with cmd+s).
  
  
  If you have FileVault, unlock it first.
  Boot into Recovery (cmd+r) directly. If it fails then repeat step 2 and retry (dGPU could get active again after
  booting into the os with AMD / NVIDIA kexts).
  Start Terminal (This commands are for AMD. If you have NVIDIA, change accordingly)
  
  diskutil cs list (find Logical Volume UUID: last item)
  diskutil coreStorage unlockVolume UUID (UUID: from previous command)
  cd /Volumes/Macintosh\ HD
  mkdir AMD_Kexts
  mv System/Library/Extensions/AMD*.* AMD_Kexts/
  reboot
  


The Result is: 

I'm using 2 hard disks, with no partition, a 120 Gb SSD for the system only and a 750 Gb drive for data. I actually don't understand the commands, I'm just following the instructions. After reboot it still hangs halfway.

Please, what should I do next?

Im using macbook pro 17" late 2011 with HD Graphics 3000/ AMD Radeon HD 6770M
The problem that you're having is that you're not quite following the instructions correctly. 

More specifically, you've run the diskutil cs list command correctly, but the purpose of running this command was to identify the Logical Volume UUID. And, the reason you needed to identify it was because you need to actually use it in the next command. 

In other words, instead of entering:

diskutil coreStorage unlockVolume UUID 

you need to enter 

diskutil coreStorage unlockVolume 3F7CB47E-F743-4DBF-9BF1-10E574F85D13

instead.

NOTE: This answer is designed to clarify how you needed to follow the instructions you're following. As your question only quotes a portion of those instructions, I cannot directly vouch for the accuracy or validity of the full instructions you're trying to follow.