arm64: dts: bitmain: Use generic "ngpios" rather than "snps,nr-gpios"

This is to remove similar errors as below:

OF: /.../gpio-port@0: could not find phandle

Commit 7569486d ("gpio: dwapb: Add ngpios DT-property support")
explained the reason of above errors well and added the generic
"ngpios" property, let's use it.
Signed-off-by: Jisheng Zhang <Jisheng.Zhang@synaptics.com>
Signed-off-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Acked-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
Link: https://lore.kernel.org/r/20201210094056.54553-1-manivannan.sadhasivam@linaro.org'
Signed-off-by: Arnd Bergmann <arnd@arndb.de>

arch/arm64/boot/dts/bitmain/bm1880.dtsi

@@ -127,7 +127,7 @@ porta: gpio-controller@0 {
 				compatible = "snps,dw-apb-gpio-port";
 				gpio-controller;
 				#gpio-cells = <2>;
-				snps,nr-gpios = <32>;
+				ngpios = <32>;
 				reg = <0>;
 				interrupt-controller;
 				#interrupt-cells = <2>;
@@ -145,7 +145,7 @@ portb: gpio-controller@0 {
 				compatible = "snps,dw-apb-gpio-port";
 				gpio-controller;
 				#gpio-cells = <2>;
-				snps,nr-gpios = <32>;
+				ngpios = <32>;
 				reg = <0>;
 				interrupt-controller;
 				#interrupt-cells = <2>;
@@ -163,7 +163,7 @@ portc: gpio-controller@0 {
 				compatible = "snps,dw-apb-gpio-port";
 				gpio-controller;
 				#gpio-cells = <2>;
-				snps,nr-gpios = <8>;
+				ngpios = <8>;
 				reg = <0>;
 				interrupt-controller;
 				#interrupt-cells = <2>;