arm-trusted-firmware-mediatek: add mt7986 UBI 1MB offset target

Add a new Trusted Firmware-A (TF-A) build profile for the MediaTek
MT7986 SoC named 'mt7986-spim-nand-ubi-1m-ddr4'.

This profile reduces the UBI starting address (UBI_START_ADDR) from
0x200000 (2MB) down to 0x100000 (1MB). This layout adjustment matches
devices like the ASUS RT-AX59U factory partition offsets and frees up
flash space for the main operating system layout.

Signed-off-by: Mikhail Zhilkin <csharper2005@gmail.com>
Link: https://github.com/openwrt/openwrt/pull/25278
Signed-off-by: Robert Marko <robimarko@gmail.com>

package/boot/arm-trusted-firmware-mediatek/Makefile

@@ -351,6 +351,17 @@ define Trusted-Firmware-A/mt7986-spim-nand-ddr4
   NAND_TYPE:=spim:2k+64
 endef
 
+define Trusted-Firmware-A/mt7986-spim-nand-ubi-1m-ddr4
+  NAME:=MediaTek MT7986 (SPI-NAND via SPIM using UBI 1MB offset, DDR4)
+  BOOT_DEVICE:=spim-nand
+  BUILD_SUBTARGET:=filogic
+  PLAT:=mt7986
+  DDR_TYPE:=ddr4
+  NAND_TYPE:=spim:2k+64
+  USE_UBI:=1
+  UBI_START_ADDR:=0x100000
+endef
+
 define Trusted-Firmware-A/mt7986-spim-nand-ubi-ddr4
   NAME:=MediaTek MT7986 (SPI-NAND via SPIM using UBI, DDR4)
   BOOT_DEVICE:=spim-nand
@@ -753,6 +764,7 @@ TFA_TARGETS:= \
 	mt7986-sdmmc-ddr4 \
 	mt7986-snand-ddr4 \
 	mt7986-spim-nand-ddr4 \
+	mt7986-spim-nand-ubi-1m-ddr4 \
 	mt7986-spim-nand-ubi-ddr4 \
 	mt7986-spim-nand-4k-ddr4 \
 	mt7987-emmc-comb \