configs/stm32mp1*_dk*: switch to external Bootlin stable toolchain

As Arnout stated[1], defconfigs should use a Bootlin toolchain (stable, glibc).

[1] https://lore.kernel.org/buildroot/e9576c4f-243b-4a89-a74d-3fee591100a8@mind.be/

Signed-off-by: Raphael Gallais-Pou <rgallaispou@gmail.com>
Signed-off-by: Julien Olivain <ju.o@free.fr>

configs/stm32mp135f_dk_defconfig

@@ -1,6 +1,8 @@
 BR2_arm=y
 BR2_cortex_a7=y
-BR2_PACKAGE_HOST_LINUX_HEADERS_CUSTOM_6_12=y
+BR2_TOOLCHAIN_EXTERNAL=y
+BR2_TOOLCHAIN_EXTERNAL_BOOTLIN=y
+BR2_TOOLCHAIN_EXTERNAL_BOOTLIN_ARMV7_EABIHF_GLIBC_STABLE=y
 BR2_GLOBAL_PATCH_DIR="board/stmicroelectronics/common/stm32mp1xx/patches"
 BR2_DOWNLOAD_FORCE_CHECK_HASHES=y
 BR2_ROOTFS_DEVICE_CREATION_DYNAMIC_MDEV=y

configs/stm32mp157a_dk1_defconfig

@@ -1,6 +1,8 @@
 BR2_arm=y
 BR2_cortex_a7=y
-BR2_PACKAGE_HOST_LINUX_HEADERS_CUSTOM_6_12=y
+BR2_TOOLCHAIN_EXTERNAL=y
+BR2_TOOLCHAIN_EXTERNAL_BOOTLIN=y
+BR2_TOOLCHAIN_EXTERNAL_BOOTLIN_ARMV7_EABIHF_GLIBC_STABLE=y
 BR2_GLOBAL_PATCH_DIR="board/stmicroelectronics/common/stm32mp1xx/patches"
 BR2_DOWNLOAD_FORCE_CHECK_HASHES=y
 BR2_ROOTFS_OVERLAY="board/stmicroelectronics/stm32mp157a-dk1/overlay/"

configs/stm32mp157c_dk2_defconfig

@@ -1,6 +1,8 @@
 BR2_arm=y
 BR2_cortex_a7=y
-BR2_PACKAGE_HOST_LINUX_HEADERS_CUSTOM_6_12=y
+BR2_TOOLCHAIN_EXTERNAL=y
+BR2_TOOLCHAIN_EXTERNAL_BOOTLIN=y
+BR2_TOOLCHAIN_EXTERNAL_BOOTLIN_ARMV7_EABIHF_GLIBC_STABLE=y
 BR2_GLOBAL_PATCH_DIR="board/stmicroelectronics/common/stm32mp1xx/patches"
 BR2_DOWNLOAD_FORCE_CHECK_HASHES=y
 BR2_ROOTFS_OVERLAY="board/stmicroelectronics/stm32mp157c-dk2/overlay/"