build_uboot.sh: use the mainline u-boot code

add changes for librem5 patch mainline u-boot
Signed-off-by: Angus Ainslie (Purism) <angus@akkea.ca>

build_uboot.sh

@@ -267,12 +267,12 @@ case ${pureos_board} in
     COPY_UBOOT=copy_uboot
     ;;
   devkit*)
-    ATF_REPO=https://source.puri.sm/Librem5/trusted-firmware-a.git
+    ATF_REPO=https://source.puri.sm/Librem5/trusted-firmware-a
     ATF_BRANCH=librem5
     ATF_PLAT=imx8mq
     DDR_FILE=files/imx-mkimage-emcraft.tar.gz
-    MKIMAGE_REPO=https://source.codeaurora.org/external/imx/imx-mkimage
-    MKIMAGE_BRANCH=imx_4.9.51_imx8m_ga
+    MKIMAGE_REPO=https://source.puri.sm/Librem5/imx-mkimage
+    MKIMAGE_BRANCH=librem5
     UBOOT_REPO=https://source.puri.sm/Librem5/uboot-imx.git
     case ${pureos_board} in
         devkit)
@@ -283,7 +283,7 @@ case ${pureos_board} in
             ;;
     esac
     CROSS_COMPILER=aarch64-linux-gnu-
-    UBOOT_BRANCH=devkit-wip
+    UBOOT_BRANCH=wip-mainline
     UBOOT_BIN=iMX8M/flash.bin
     UBOOT_DTB=librem5-evk.dtb
     ARCH=arm