msm: kgsl: Fix linked sysfs files

kernfs_create_link is an unexported function so we need a workaround.
Luckily most of the "linked" sysfs files are our own, so we can just
create new attributes with the same callback functions.  We're not
so lucky with the devfreq nodes but they are optional so we can
omit them when we are building as a module.

Change-Id: Ic0dedbad7e5f4e28a62ce57abb6451f4865d37ab
Signed-off-by: Jordan Crouse <jcrouse@codeaurora.org>