msm: kgsl: Modify which MMU clocks are enabled/disabled

There is no need to try to attach a clock if it is already attached,
or detach a clock if it is already detached. Restructure this
logic to only attach/detach the clocks when needed. As well as
protect ourselves using the MMU lock more readily.

Signed-off-by: Carter Cooper <ccooper@codeaurora.org>
Change-Id: Ib5edfe7800cc246bc4b5e9aca8e02621aa6f7c3c