In the meantime, I'm going to try the suggestion of using Catalyst drivers first before venturing into kernel building since the laptop's graphics is behaving oddly apart from the resume problem.
As an update, downloading the latest AMD fglrx 14.4rev2 drivers and installing it fixed the unable to resume problem to some extend. pm-hibernate will work properly but pm-suspend will wake up to a blank screen which apparently is a common enough problem from googling. Might be something to do with systemd based on this archlinux thread https://bbs.archlinux.org/viewtopic.php?id=178450
However, in my case, this appears to be circumvented in runlevel 5 (runlevel 3 gets stuck until I type blind or ssh in to reboot/hibernate the machine). In runlevel 5, the screen flashes on briefly, then go blank, after a while it comes back and abrt reports a crash with plymouthd. Seems like X will retry in this situation so it causes the display to come back.
If it is of any use, I could send the abrt report somewhere.