build: Fix usage of hardcoded zephyr.{elf,bin,hex} on faze board

Make similar fix for faze board to use ${KERNEL_BIN_NAME} and
${KERNEL_HEX_NAME} variables as its possible to rename the executable
binary via CONFIG_KERNEL_BIN_NAME.

This fixes tests/misc/test_build/buildsystem.kconfig.utf8_in_values

Fixes #28013

Signed-off-by: Kumar Gala <kumar.gala@linaro.org>