package/iprutils: Add IBM Power RAID utilities

[Thomas: add patch to allow passing CFLAGS from the environment, use
TARGET_CONFIGURE_OPTS instead of manually passing CC/LD, add upstream
URL in Config.in, use the Makefile install target instead of
open-coding the installation in iprutils.mk.]

Signed-off-by: Jeremy Kerr <jk@ozlabs.org>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>