clk: qcom: support for 2 bit PLL post divider

Current PLL driver only supports 4 bit PLL post divider so
modified the PLL divider operations to support 2 bit PLL
post divider.

Signed-off-by: Abhishek Sahu <absahu@codeaurora.org>
Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>