mmc: sdhci-msm: Add support to vote for vdd io parent regulator

As per vdd io parent regulator design, in active use cases
L7A needs to be on when vdd io regulator is operating at
2.96V, and has to be off when io regulator is operating at
1.8V.

To implement above add support to vote for vdd io parent
regulator.

Change-Id: I47f73a0d6733d96ec9ed41dd2522c85646a65d18
Signed-off-by: Ram Prakash Gupta <rampraka@codeaurora.org>