msm: kgsl: Ensure correct enable sequence for 2D core clock

Calling clk_set_rate() for both AXI & 2D core clocks without putting
them in async mode causes 2D core hang. Since AXI & 2D core clocks
are in sync mode, ensure that clk_set_rate() is called only for AXI
& 2D core clock is enabled only after it is prepared.

Change-Id: I4634e2342d62ce16ad7afc748b10b0573fbfd913
CRs-fixed: 385393
Signed-off-by: Ranjhith Kalisamy <ranjhith@codeaurora.org>