msm: kgsl: Disable rbbm countable on a540

The RBBM_ALWAYS_COUNT countable does not function properly
when top level clock gating is enabled. Return -EINVAL
when user requests this perfcounter.

CRs-Fixed: 1038778
Change-Id: I48d560ab2caa6ea467ac56bf0d323937a475cdde
Signed-off-by: Harshdeep Dhatt <hdhatt@codeaurora.org>