clk: qcom: clk-spmi-pmic-div: add support for clock-output-names

Some boards utilize several PMICs which contain clock divider
peripherals.  Add support for the clock-output-names property
so that unique names can be specified for each divider clock.
If clock-output-names is not specified, then the clock names
will be div_clkN where N=1 to qcom,num-clkdivs.

Change-Id: I66b5fcd0a3890886fe1e8cd85b15ada8a55ecb0f
Signed-off-by: David Collins <collinsd@codeaurora.org>