Hi, 
I've got a very similar laptop, also a Dell 5558, but I'm having issues getting started. Perhaps the wrong version of the bios? 
I'm trying to set the video startup memory 
After some trying I was not able to find the setup key in the bios that was described. I finally managed to get booted to EFI and setup_var isn't recognised as a command. 
I'm on bios version A10. 
Has anyone else had similar issues? 
Got the efi shell:) 
now looking for the variable name to set video memory 
Got it! I found reference to 0x15b and 0x15c, tried both, 0x15c left the system unbootable, I think that must be just for dedicated graphics, I only have the Intel. got it up running and 0x15b set at 0x3. Windows reports 192mb but I confirmed 0x3. ) 
Wish me luck, haha