msm_fb: mdss: Remove spinlocks for set_rate and clk_enable APIs

The clk_set_rate APIs should not be called in atomic context.
clk_enable APIs doesn't need to be in atomic context. Add code
to remove spinlocks for these clock APIs.

Change-Id: If5e543135bda681ee8ddae35ab91288f535a9e9a
Signed-off-by: Chandan Uddaraju <chandanu@codeaurora.org>