buildroot

btrfs-progs: bump to version 4.7.2

Drop all of the upstreamed patches (not precisely in the same form) and
rebase the only required patch for proper static builds with staging
libs required by other packages.
Build-tested for arm-glibc, arm-uclibc, arm-musl and arm-uclibc-static.

Signed-off-by: Gustavo Zacarias <gustavo@zacarias.com.ar>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>