I've got a Latitude E6540 with Intel HD4600 + AMD 8790M graphics and I've been trying to disable the AMD 8790M. I've tried for about 2 weeks and once I disable it, the OS X will get high fan speed and auto shut down. So please take a look at it.
origin.zip
This is the zip file of original DSDT and SSDTs extracted from clover---F4 key.