i2c-tools: use update-alternatives

i2c-tools: use update-alternatives

i2cget, i2cset, i2cdump and i2cdetect may also be provided by Busybox
when CONFIG_I2CGET, CONFIG_I2CSET, CONFIG_I2CDUMP and CONFIG_I2CDETECT
are enabled respectively.

Busybox has a priority of 50.

Prior to the patch building core-image-minimal with

    IMAGE_INSTALL_append = " busybox"
    IMAGE_INSTALL_append = " i2c-tools"

in local.conf produced the warnings

    WARNING: core-image-minimal-1.0-r0 do_rootfs: busybox.postinst returned 1, marking as unpacked only, configuration required on target.
    WARNING: core-image-minimal-1.0-r0 do_rootfs: Intentionally failing postinstall scriptlets of ['busybox'] to defer them to first boot is deprecated. Please place them into pkg_postinst_ontarget_${PN} ().
    If deferring to first boot wasn't the intent, then scriptlet failure may mean an issue in the recipe, or a regression elsewhere.
    Details of the failure are in /path/to/poky/build/tmp-glibc/work/qemux86-oe-linux/core-image-minimal/1.0-r0/temp/log.do_rootfs.
    WARNING: core-image-minimal-1.0-r0 do_rootfs: [log_check] core-image-minimal: found 1 warning message in the logfile:
    [log_check] WARNING: Intentionally failing postinstall scriptlets of ['busybox'] to defer them to first boot is deprecated. Please place them into pkg_postinst_ontarget_${PN} ().

where log.do_rootfs contained

    update-alternatives: Error: not linking /path/to/poky/build/tmp-glibc/work/qemux86-oe-linux/core-image-minimal/1.0-r0/rootfs/usr/sbin/i2cget to /bin/busybox.nosuid since /path/to/poky/build/tmp-glibc/work/qemux86-oe-linux/core-image-minimal/1.0-r0/rootfs/usr/sbin/i2cget exists and is not a link

and similarly for i2cset, i2cdump and i2cdetect when a workspace layer
created by devtool contained

    cat workspace/appends/busybox_%.bbappend
    FILESEXTRAPATHS_prepend := "${THISDIR}/${PN}:"

    SRC_URI_append = " file://i2c.cfg"

and

    cat workspace/appends/busybox/i2c.cfg
    CONFIG_I2CGET=y
    CONFIG_I2CSET=y
    CONFIG_I2CDETECT=y
    CONFIG_I2CDUMP=y

Signed-off-by: Hannu Lounento <hannu.lounento@vaisala.com>
Signed-off-by: Ross Burton <ross.burton@intel.com>