mmc: core: add the capability for broken voltage.

This patch is added the MMC_CAP2_BROKEN_VOLTAGE.

"There is an understood mismatch between the voltage the host controller is set to and the voltage supplied to the card by a fixed voltage regulator. Teaching the driver to accept the mismatch is overly complicated. Instead just accept the regulator's voltage."

if the voltage didn't satisfy between min_uV and max_uV, try to change the voltage in core.c.
When change the voltage, maybe use the regulator_set_voltage().

In regulator_set_voltage(), check the below condition.

	/* sanity check */
	if (!rdev->desc->ops->set_voltage &&
	    !rdev->desc->ops->set_voltage_sel) {
		ret = -EINVAL;
		goto out;
	}

If Some-board should use the fixed-regulator, always return -EINVAL. Then, eMMC didn't initialize always.

So if use the fixed-regulator or etc, we need to add the MMC_CAP2_BROKEN_VOLTAGE.

---
 drivers/mmc/core/core.c  |    4 ++++
 include/linux/mmc/host.h |    1 +
 2 files changed, 5 insertions(+), 0 deletions(-)

index bec0bf2..6848789 100644
@@ -1121,6 +1121,10 @@ int mmc_regulator_set_ocr(struct mmc_host *mmc,
 		 * might not allow this operation
 		 */
 		voltage = regulator_get_voltage(supply);
+
+		if (mmc->caps2 & MMC_CAP2_BROKEN_VOLTAGE)
+			min_uV = max_uV = voltage;
+
 		if (voltage < 0)
 			result = voltage;
 		else if (voltage < min_uV || voltage > max_uV)

index dd13e05..5659aee 100644
@@ -257,6 +257,7 @@ struct mmc_host {
 #define MMC_CAP2_HS200_1_2V_SDR	(1 << 6)        /* can support */
 #define MMC_CAP2_HS200		(MMC_CAP2_HS200_1_8V_SDR | \
 				 MMC_CAP2_HS200_1_2V_SDR)
+#define MMC_CAP2_BROKEN_VOLTAGE	(1 << 7)	/* Use the broken voltage */
 
 	mmc_pm_flag_t		pm_caps;	/* supported pm features */