msm: dma: Use clk_prepare and clk_unprepare

clk_prepare and clk_unprepare are now required to be called before
clk_enable and after clk_disable. Do this for the dma driver.
Additionally, split the msm_dmov_clk_toggle function into two, since we
always know the value of the second argument at compile time.

CRs-Fixed: 366651
Change-Id: I0ed229187f49352cfe59cbbf211f5cdabfe06a9d
Signed-off-by: Jeff Ohlstein <johlstei@codeaurora.org>