boards: set CONFIG_BUILD_OUTPUT_HEX for TI boards

After changes in 3124c02987071b045b33bbfa2d12606b2ff0a757,
CONFIG_BUILD_OUTPUT_HEX now needs to be set in the boards' default
configuration in order for the runner to be passed the path to the
hex file being loaded.

Fixes #28203

Signed-off-by: Vincent Wan <vwan@ti.com>
4 files changed