msm: kgsl: Create cff_dump file only if CONFIG_MSM_KGSL_CFF_DUMP is enabled

Create /sys/kernel/debug/kgsl/kgsl-3d0/cff_dump file only if
CONFIG_MSM_KGSL_CFF_DUMP option is enabled. Do not
create this file if the rest of cff is not enabled.

CRs-fixed: 651827
Change-Id: If55b6d5d8d4ed5a662c61ed3bb7f710414bdc034
Signed-off-by: Harsh Vardhan Dwivedi <hdwivedi@codeaurora.org>