clk: qcom: add read-only alpha pll post divider operations

Some of the divider settings are preconfigured and should not
be changed by the clock framework during frequency change. This
patch adds the read-only divider operation for QCOM alpha pll
post divider which is equivalent to generic divider operations in
'commit 79c6ab50 ("clk: divider: add CLK_DIVIDER_READ_ONLY flag")'.

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