eal: simplify meson build of common directory

eal: simplify meson build of common directory

The variable common_sources allows to change the list of common files
from an arch-specific or OS-specific meson file.
For consistency and least surprise principle, this variable is removed.
Now the list of common sources is defined only in common/meson.build.
As a consequence, the temporary list of files which are currently supported
on Windows, is moved from windows/eal/meson.build.

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