dtc: bump version to 1.4.4

dtc: bump version to 1.4.4

Adds overlay support.

Drop the non-upstreamed 0002-extra-cflags.patch and instead simply pass the
needed CFLAGS as make arguments.  Passing the full upstream warning flags
are not important in the Buildroot context, so this is simpler than
maintaining a patch.

Cc: "Yann E. MORIN" <yann.morin.1998@free.fr>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>
Reviewed-by: Matt Weber <matthew.weber@rockwellcollins.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>