bitbake.conf: add bunzip2 in HOSTTOOLS

bitbake.conf: add bunzip2 in HOSTTOOLS

rpm2cpio.sh can make calls to bunzip2 to uncompress the RPM payload that
conform the cpio file.

bzip2 is already part of HOSTTOOLS, as a link to the system installed
bzip2.

This patch add bunzip2 in HOSTOOLS list as a non-optional binary, so is
available to rpm2cpio.sh when it is required.

The currect rpm2cpio.sh has other calls to gunzip (present in HOSTOOLS),
xzcat (missing), unlzma (missing) and unzstd (present in HOSTTOOLS since
bff58d337890e804d33d7decbaa46065a4d3bba4)

Adding the missing ones will not add any new host dependency as xz-utils
is already listed as a requirement.

Signed-off-by: Alberto Planas <aplanas@suse.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
(cherry picked from commit fd376a11ed8d1b79633c2572ec0b4341d3ca2f1c)
Signed-off-by: Steve Sakoman <steve@sakoman.com>