clk: qcom: support for alpha mode configuration

The current configuration does not fully configure PLL alpha mode
and values so this patch

1. Configures PLL_ALPHA_VAL_U for PLL which supports 40 bit alpha.
2. Adds alpha enable and alpha mode configuration support.

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