clk: qcom: clk-alpha-pll: Add support for FSM legacy mode

The Lucid PLL could require the FSM legacy mode bit to be set for the
PLL to be operational, thus add support and set the same when the flag
is set.

While at it also update the Zonda disable function to remove the
additional offset usage.

Change-Id: I3ed4b6c38a1769c5021f17e0115215eab615ab62
Signed-off-by: Taniya Das <tdas@codeaurora.org>