configure: use autoconf to generate configure

Create configure.ac, an autoconf script to generate ./configure
This will be needed by a subsequent patch to properly handle
--build and --host, and more tests, when the kconfig stuff will
be installed pre-built.

Signed-off-by: "Yann E. MORIN" <yann.morin.1998@anciens.enib.fr>

 # m68k specific configuration file

 ## depends on EXPERIMENTAL

 ##

 ## select ARCH_SUPPORTS_32

 ## select ARCH_DEFAULT_32

 ## select ARCH_DEFAULT_BE

 ## select ARCH_SUPPORTS_WITH_CPU

 ##

 ## help The m68k architecture