Move fdt_path_offset alias tests to right tests section

The test script includes several specific tests for the handling of aliases
in fdt_path_offset().  These are primarily tests of the fdt_path_offset()
libfdt function itself, although dtc is used to generate a test file for
convenience.

Move these from the dtc tests section to the libfdt tests section
accordingly.

Signed-off-by: David Gibson <david@gibson.dropbear.id.au>