efi: efi-stub-helper cleanup

An #ifdef CONFIG_ARM clause in efi-stub-helper.c got included with some
of the generic stub rework by Roy Franz. Drop it here to make subsequent
patches less confusing.

Also, In handle_cmdline_files(), fh is not initialized, and while the
overall logic around this handling appears safe, gcc does not always
pick this up. Initialize to NULL to remove the resulting warning.

Signed-off-by: Leif Lindholm <leif.lindholm@linaro.org>
Signed-off-by: Matt Fleming <matt.fleming@intel.com>