mmc: sd: Handle UHS-I voltage signaling without power cycle

Some boards have SD card connectors where the power rail cannot be switched
off by the driver. However there are various circumstances when a card
might be re-initialized, such as after system resume, warm re-boot, or
error handling. However, a UHS card will continue to use 1.8V signaling
unless it is power cycled.

If the card has not been power cycled, it may still be using 1.8V
signaling. According to the SD spec., the Bus Speed Mode (function group 1)
bits 2 to 4 are zero if the card is initialized at 3.3V signal level. Thus
they can be used to determine if the card has already switched to 1.8V
signaling. Detect that situation and try to initialize a UHS-I (1.8V)
transfer mode.

Signed-off-by: Tanmay Kathpalia <tanmay.kathpalia@altera.com>
Signed-off-by: Peng Fan <peng.fan@nxp.com>

include/mmc.h

@@ -759,6 +759,9 @@ struct mmc {
 #endif
 	u8 *ext_csd;
 	u32 cardtype;		/* cardtype read from the MMC */
+#if CONFIG_IS_ENABLED(MMC_UHS_SUPPORT)
+	u32 sd3_bus_mode;	/* Supported UHS-I bus speed modes */
+#endif
 	enum mmc_voltage current_voltage;
 	enum bus_mode selected_mode; /* mode currently used */
 	enum bus_mode best_mode; /* best mode is the supported mode with the