ARM: dts: at91: remove duplicated entries

Remove duplicated DTC_FLAGS_<board> := -@ entries which intends to enable
the building of device tree overlays.
Commit 724ba675 ("ARM: dts: Move .dts files to vendor sub-directories")
added those entries at the beginning of file w/o removing the already
available entries spread though file.
Acked-by: Nicolas Ferre <nicolas.ferre@microchip.com>
Link: https://lore.kernel.org/r/20230721053918.33944-1-claudiu.beznea@tuxon.devSigned-off-by: Claudiu Beznea <claudiu.beznea@tuxon.dev>

arch/arm/boot/dts/microchip/Makefile

 # SPDX-License-Identifier: GPL-2.0
+# Enables support for device-tree overlays
 DTC_FLAGS_at91-sam9x60_curiosity := -@
 DTC_FLAGS_at91-sam9x60ek := -@
 DTC_FLAGS_at91-sama5d27_som1_ek := -@
@@ -54,21 +55,9 @@ dtb-$(CONFIG_SOC_AT91SAM9) += \
 	at91sam9g35ek.dtb \
 	at91sam9x25ek.dtb \
 	at91sam9x35ek.dtb
-# Enables support for device-tree overlays
-DTC_FLAGS_at91-sam9x60_curiosity := -@
-DTC_FLAGS_at91-sam9x60ek := -@
 dtb-$(CONFIG_SOC_SAM9X60) += \
 	at91-sam9x60_curiosity.dtb \
 	at91-sam9x60ek.dtb
-# Enables support for device-tree overlays
-DTC_FLAGS_at91-sama5d27_som1_ek := -@
-DTC_FLAGS_at91-sama5d27_wlsom1_ek := -@
-DTC_FLAGS_at91-sama5d2_icp := -@
-DTC_FLAGS_at91-sama5d2_ptc_ek := -@
-DTC_FLAGS_at91-sama5d2_xplained := -@
-DTC_FLAGS_at91-sama5d3_eds := -@
-DTC_FLAGS_at91-sama5d3_xplained := -@
-DTC_FLAGS_at91-sama5d4_xplained := -@
 dtb-$(CONFIG_SOC_SAM_V7) += \
 	at91-kizbox2-2.dtb \
 	at91-kizbox3-hs.dtb \
@@ -95,8 +84,6 @@ dtb-$(CONFIG_SOC_SAM_V7) += \
 	at91-sama5d4_xplained.dtb \
 	at91-sama5d4ek.dtb \
 	at91-vinco.dtb
-# Enables support for device-tree overlays
-DTC_FLAGS_at91-sama7g5ek := -@
 dtb-$(CONFIG_SOC_SAMA7G5) += \
 	at91-sama7g5ek.dtb