ARM: at91/dt: add always-on to 1.8V regulator

As the SDHCI controller needs the 1.8V line to be always enabled for some eMMC
configurations, set the proper "regulator-always-on" property to the board DTS
files.
Note that the sdhci classical regulator definitions doesn't suit our controller
for this 1.8V purpose.
Signed-off-by: NNicolas Ferre <nicolas.ferre@atmel.com>
Acked-by: NLudovic Desroches <ludovic.desroches@atmel.com>
Signed-off-by: NAlexandre Belloni <alexandre.belloni@free-electrons.com>

arch/arm/boot/dts/at91-sama5d2_xplained.dts

@@ -184,6 +184,7 @@
 							regulator-name = "VDD_SDHC_1V8";
 							regulator-min-microvolt = <1800000>;
 							regulator-max-microvolt = <1800000>;
+							regulator-always-on;
 						};
 					};
 				};