linux-zigbee: new package

linux-zigbee: new package

linux-zigbee is a mix of utility tools that implements a 802.15.4 stack
along with a usefull library for any program that would need to use this
stack.

Note that the name is mislead, for licensing reason, this does *NOT*
implement the ZigBee protocol.

[Thomas:
 - add dependency on threads, propagated from libnl
 - improve the Config.in description by borrowing more text from the
   upstream website
 - fix the prompt of sub-options to be more consistent, and add help
   texts where appropriate
 - fix indentation of the BR2_PACKAGE_LINUX_ZIGBEE_TESTS option help
   text
 - add missing dependencies on host-pkgconf, host-flex and host-bison
 - add missing SoB line in the patch disabling test-serial. Maxime is
   a well-known contributor, so I assumed we had his SoB.
 - fix indentation of <pkg>_CONF_OPT.
 - remove <pkg>_INSTALL_STAGING = YES since the package does not
   install any library, and the two headers it installs are available
   through the toolchain kernel headers.
 - add comment to explain <pkg>_AUTORECONF = YES.]

Signed-off-by: Maxime Hadjinlian <maxime.hadjinlian@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>