msm: kgsl: Add user specified GPU object metadata

Allow the user to optionally specify up to 64 bytes of metadata
to describe the memory object. The strings for each object are
printed in the /d/kgsl/<proc>/mem file.  The user may specify
anything they wish but we strip out non-printable characters
to avoid any evil intent.

Change-Id: Ic0dedbad2c5d80aacd3a2292346a9075bc7f543b
Signed-off-by: Jordan Crouse <jcrouse@codeaurora.org>