clk: qcom: add parent map for regmap mux

Currently the driver assumes the register configuration value
is identical to its index in the parent map. This patch adds
the parent map field in regmap mux clock node which contains
the mapping of parent index with actual register configuration
value. If regmap node contains this parent map then the
configuration value will be taken from this
parent map instead of simply writing the index value.

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