ahci: increase spin-up timeout to 20 sec

Based on Linux libata code, most drives are less than 10 sec, but some
need up to 20 sec.

Signed-off-by: Rob Herring <rob.herring@calxeda.com>
Reviewed-by: Tom Rini <trini@ti.com>

drivers/block/ahci.c

@@ -38,7 +38,7 @@ hd_driveid_t *ataid[AHCI_MAX_PORTS];
 #endif
 
 /* Maximum timeouts for each event */
-#define WAIT_MS_SPINUP	10000
+#define WAIT_MS_SPINUP	20000
 #define WAIT_MS_DATAIO	5000
 #define WAIT_MS_FLUSH	5000
 #define WAIT_MS_LINKUP	4