moveconfig: Support providing a path to the defconfig files

It is convenient to provide the full patch to the defconfig files in some
situations, e.g. when the file was generated by a shell command (e.g.
'ls configs/zynq*').

Add support for this, and move the globbing code into a function with its
own documentation.

Signed-off-by: Simon Glass <sjg@chromium.org>