ARM: dts: at91: sama7g5ek: to not touch slew-rate for SDMMC pins

With commit c709135e ("pinctrl: at91-pio4: add support for slew-rate")
and commit cbde6c82 ("pinctrl: at91-pio4: Fix slew rate disablement")
the slew-rate is enabled by default for each configured pin. The datasheet
specifies at chapter "Output Driver AC Characteristics" that HSIO
drivers (use in SDMMCx and QSPI0 peripherals), don't have a slewrate
setting but are rather calibrated against an external 1% resistor mounted
on the SDMMCx_CAL or QSPI0_CAL pins. Depending on the target signal
frequency and the external load, it is possible to adjust their target
output impedance. Thus set slew-rate = <0> for SDMMC (QSPI is not enabled
at the moment in device tree).

Fixes: 7540629e ("ARM: dts: at91: add sama7g5 SoC DT and sama7g5-ek")
Signed-off-by: Claudiu Beznea <claudiu.beznea@microchip.com>
Signed-off-by: Nicolas Ferre <nicolas.ferre@microchip.com>
Link: https://lore.kernel.org/r/20210915074836.6574-3-claudiu.beznea@microchip.com

arch/arm/boot/dts/at91-sama7g5ek.dts

@@ -558,6 +558,7 @@ cmd_data {
 				 <PIN_PA8__SDMMC0_DAT5>,
 				 <PIN_PA9__SDMMC0_DAT6>,
 				 <PIN_PA10__SDMMC0_DAT7>;
+			slew-rate = <0>;
 			bias-pull-up;
 		};
 
@@ -565,6 +566,7 @@ ck_cd_rstn_vddsel {
 			pinmux = <PIN_PA0__SDMMC0_CK>,
 				 <PIN_PA2__SDMMC0_RSTN>,
 				 <PIN_PA11__SDMMC0_DS>;
+			slew-rate = <0>;
 			bias-pull-up;
 		};
 	};
@@ -576,6 +578,7 @@ cmd_data {
 				 <PIN_PC0__SDMMC1_DAT1>,
 				 <PIN_PC1__SDMMC1_DAT2>,
 				 <PIN_PC2__SDMMC1_DAT3>;
+			slew-rate = <0>;
 			bias-pull-up;
 		};
 
@@ -584,6 +587,7 @@ ck_cd_rstn_vddsel {
 				 <PIN_PB28__SDMMC1_RSTN>,
 				 <PIN_PC5__SDMMC1_1V8SEL>,
 				 <PIN_PC4__SDMMC1_CD>;
+			slew-rate = <0>;
 			bias-pull-up;
 		};
 	};
@@ -595,11 +599,13 @@ cmd_data {
 				 <PIN_PD6__SDMMC2_DAT1>,
 				 <PIN_PD7__SDMMC2_DAT2>,
 				 <PIN_PD8__SDMMC2_DAT3>;
+			slew-rate = <0>;
 			bias-pull-up;
 		};
 
 		ck {
 			pinmux = <PIN_PD4__SDMMC2_CK>;
+			slew-rate = <0>;
 			bias-pull-up;
 		};
 	};