clk: qcom: sm6150: define vdd_levels enum and vdd_corner[] map

Define a vdd_levels enum and vdd_corner[] mapping table which can
be used by clock controller drivers to configure the vdd_class
associated with their clocks.

Change-Id: I7b1ad5f51c414694bc9d5101afc411b1d63bad42
Signed-off-by: Veera Vegivada <vvegivad@codeaurora.org>