mmc: sdhci-msm: support dual voltage pad for eMMC

Only 1.8V is used on IO pad lines for eMMCs' on msm platforms. So this
means for any SDHC core on msm platforms used with eMMCs' should have
PAD_PWR_SWITCH bit set indicating that 1.8V is used for IO lines. So far
this did not matter as all eMMCs' SDHC pads were single voltage and the
PAD_PWR_SWTICH bit did not make a difference.

But when a SDHC core that supports dual voltage pad is used for
initializing eMMC, the BUS_ON pwr_irq generated would cause the pad
to be set at a logical HIGH in the driver (as it should since the
bus is being turned ON) but then the driver does not set or clear
the PAD_PWR_SWITCH for eMMCs which causes the communication between
the host and card to break down. So even though the IO pad is driven
at 1.8V, the host is not told that it should switch to 1.8V IO from
3.0V (default).

This does not matter for SD cards for when they are turned ON, they always
start with 3.0V on IO pad. But for eMMC instead of not setting or clearing
the PAD_PWR_SWITCH bit when the bus is turned ON, check the voltage being
supplied on the IO pad and based on that set or clear the PAD_PWR_SWITCH.

Change-Id: I7756731760298c6766d00a22160c6328faaaf4a7
Signed-off-by: Krishna Konda <kkonda@codeaurora.org>