ibrcommon: new package

[Thomas:
  - add package in package/Config.in, to make it visible in menuconfig
  - make the openssl, libnl and libxml2 dependencies optional, since
    they are definitely not mandatory
  - add README to the license files, since it contains useful
    licensing related information.
  - remove custom INSTALL_STAGING_OPTS and INSTALL_TARGET_OPTS since
    the package uses automake.
  - add missing final newline in Config.in and .mk file.]

Signed-off-by: Tom Sparks <tom_a_sparks@yahoo.com.au>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>