eal: move common header files

The EAL API (with doxygen documentation) is moved from
common/include/ to include/, which makes more clear that
it is the global API for all environments and architectures.

Note that the arch-specific and OS-specific include files are not
in this global include directory, but include/generic/ should
cover the doxygen documentation for them.

Signed-off-by: Thomas Monjalon <thomas@monjalon.net>
Acked-by: David Marchand <david.marchand@redhat.com>