Enable all the mmc/sd controllers, because there's no telling which ones

any given board will be using.

Yes, changing source is an unusually primitive power control implementation.

sys/arm/freescale/imx/imx6_ccm.c

@@ -95,7 +95,7 @@ ccm_init_gates(struct ccm_softc *sc)
 	WR4(sc, CCM_CCGR3, 0x3ff00000); /* DDR memory controller */
 	WR4(sc, CCM_CCGR4, 0x0000f300); /* pl301 bus crossbar */
 	WR4(sc, CCM_CCGR5, 0x0f000000); /* uarts */
-	WR4(sc, CCM_CCGR6, 0x000000cc); /* usdhc 1 & 3 */
+	WR4(sc, CCM_CCGR6, 0x000000ff); /* usdhc 1-4 */
 }
 
 static int