configs/avenger96_defconfig: bump ATF version to 2.9 for binutils 2.39+ support

This new binutils version break the ATF build due to new linker warnings:

 ld.bfd: warning: bl2.elf has a LOAD segment with RWX permissions

From [1]
"Users of GNU ld (BPF) from binutils 2.39+ will observe multiple instaces
 of a new warning when linking the bl*.elf in the form:

 ld.bfd: warning: stm32mp1_helper.o: missing .note.GNU-stack section implies executable stack
 ld.bfd: NOTE: This behaviour is deprecated and will be removed in a future version of the linker
 ld.bfd: warning: bl2.elf has a LOAD segment with RWX permissions
 ld.bfd: warning: bl32.elf has a LOAD segment with RWX permissions

These new warnings are enbaled by default to secure elf binaries:
  - https://sourceware.org/git/?p=binutils-gdb.git;a=commit;h=ba951afb99912da01a6e8434126b8fac7aa75107
  - https://sourceware.org/git/?p=binutils-gdb.git;a=commit;h=0d38576a34ec64a1b4500c9277a8e9d0f07e6774
"

Bump the ATF custom version to 2.9 for binutils 2.39+ support.

Fixes:
https://gitlab.com/buildroot.org/buildroot/-/jobs/4889436283

Signed-off-by: Romain Naour <romain.naour@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>

configs/avenger96_defconfig

@@ -17,7 +17,7 @@ BR2_TARGET_ROOTFS_EXT2_SIZE="120M"
 # BR2_TARGET_ROOTFS_TAR is not set
 BR2_TARGET_ARM_TRUSTED_FIRMWARE=y
 BR2_TARGET_ARM_TRUSTED_FIRMWARE_CUSTOM_VERSION=y
-BR2_TARGET_ARM_TRUSTED_FIRMWARE_CUSTOM_VERSION_VALUE="v2.2"
+BR2_TARGET_ARM_TRUSTED_FIRMWARE_CUSTOM_VERSION_VALUE="v2.9"
 BR2_TARGET_ARM_TRUSTED_FIRMWARE_PLATFORM="stm32mp1"
 BR2_TARGET_ARM_TRUSTED_FIRMWARE_ADDITIONAL_VARIABLES="STM32MP_SDMMC=1 AARCH32_SP=sp_min DTB_FILE_NAME=stm32mp157a-avenger96.dtb"
 BR2_TARGET_ARM_TRUSTED_FIRMWARE_DEBUG=y