msm: VPU: Make debugfs support conditional on kernel config

Previously, debugfs support was always included in the
vpu driver. This change makes debugfs support optional
as it is only required for debugging purposes.

Change-Id: I661185d838ee48a3b783c0b7952a33e2c9ab1918
Signed-off-by: Mohammed Sardar <msardar@codeaurora.org>