dtc: bump version to 1.4.1

Patch 0001-separate-lib-install.patch is no longer needed,
original Makefile already contains separate install-lib target
(but build always complete default target).

Remove superfluous CFLAGS setting.

Adjust 0002-extra-cflags.patch.

Signed-off-by: Peter Seiderer <ps.report@gmx.net>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>