boards/tiva: change default toolchain for tm4c123g to GNU EABI

fixes: #18668

Signed-off-by: Daniel Monteiro <monteiroquiet@gmail.com>

Author: TheFakeMontyOnTheRun

boards/arm/tiva/tm4c123g-launchpad/configs/nsh/defconfig

@@ -17,7 +17,6 @@ CONFIG_ARCH_CHIP_TM4C123=y
 CONFIG_ARCH_CHIP_TM4C123GH6PM=y
 CONFIG_ARCH_CHIP_TM4C=y
 CONFIG_ARCH_STACKDUMP=y
-CONFIG_ARM_TOOLCHAIN_BUILDROOT_OABI=y
 CONFIG_BOARD_LOOPSPERMSEC=4531
 CONFIG_BUILTIN=y
 CONFIG_INIT_ENTRYPOINT="nsh_main"