tools/testing: abstract two init.h into common include directory

Currently we have two test suits define its own init.h. This is a little
redundant.

Let's create a init.h in common include directory and merge these two
into it.

Signed-off-by: Wei Yang <richard.weiyang@gmail.com>
CC: Mike Rapoport <rppt@kernel.org>
CC: Liam R. Howlett <Liam.Howlett@oracle.com>
Link: https://lore.kernel.org/r/20240712035138.24674-3-richard.weiyang@gmail.com


Signed-off-by: Mike Rapoport (Microsoft) <rppt@kernel.org>