gpu: finish gpu control interface

Use proper paths to the gpu_control driver since its dircetly linked
to /proc/gpu/*
Also set up some sort of check operation to show the current state of
the feature
memory: cleanup memory interface

* added dyn_fsync checkbox
* deleted useless placeholders
* updated fstrim operation a bit (still a buggy)
memory: make zcache work

Inspired by the work from xdaid, pretty simple thanks to the generic
shell
backend :)