mmc: sdhci: if MAX_CURRENT is 0, try getting current from regulator

The sd host controller spec indicates the the MAX_CURRENT value may
be returned as 0.  In this case other methods need to be used to
return the current.  If 0 is returned and there is a regulator,
ask the regulator for how much current is available.

Signed-off-by: Philip Rakity <prakity@marvell.com>
Signed-off-by: Mark F. Brown <mark.brown314@gmail.com>
Reviewed-by: Aaron Lu <aaron.lu@amd.com>
Signed-off-by: Chris Ball <cjb@laptop.org>

drivers/mmc/host/sdhci.h

@@ -205,6 +205,7 @@
 #define SDHCI_CAPABILITIES_1	0x44
 
 #define SDHCI_MAX_CURRENT		0x48
+#define  SDHCI_MAX_CURRENT_LIMIT	0xFF
 #define  SDHCI_MAX_CURRENT_330_MASK	0x0000FF
 #define  SDHCI_MAX_CURRENT_330_SHIFT	0
 #define  SDHCI_MAX_CURRENT_300_MASK	0x00FF00