arm64: dts: imx8mq-librem5: Drop interrupt-names in PMIC

The 'interrupt-names' property is not described in dtschema, not used by
the driver and does not really make sense as its value is simple 'irq'.
Drop it to fix dtbs_check warnings like:

  arch/arm64/boot/dts/freescale/imx8mq-librem5-devkit.dt.yaml:
    pmic@4b: 'interrupt-names' does not match any of the regexes: 'pinctrl-[0-9]+'
Signed-off-by: Krzysztof Kozlowski <krzk@kernel.org>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>

arch/arm64/boot/dts/freescale/imx8mq-librem5-devkit.dts

@@ -289,7 +289,6 @@ pmic: pmic@4b {
 		clock-output-names = "pmic_clk";
 		interrupt-parent = <&gpio1>;
 		interrupts = <3 GPIO_ACTIVE_LOW>;
-		interrupt-names = "irq";
 		rohm,reset-snvs-powered;
 
 		regulators {

arch/arm64/boot/dts/freescale/imx8mq-librem5.dtsi

@@ -640,7 +640,6 @@ pmic: pmic@4b {
 		clock-output-names = "pmic_clk";
 		interrupt-parent = <&gpio1>;
 		interrupts = <7 GPIO_ACTIVE_LOW>;
-		interrupt-names = "irq";
 		rohm,reset-snvs-powered;
 
 		regulators {