zefi.py: Use cross compiler while building zephyr

Currently, zefi.py takes host GCC OBJCOPY as
default. Fixing the script to use CMAKE_C_COMPILER
and CMAKE_OBJCOPY.

Fixes: #27047

Signed-off-by: Spoorthy Priya Yerabolu <spoorthy.priya.yerabolu@intel.com>
3 files changed