gnu: Update packages to use 'non-copyleft' instead of 'bsd-style'.

gnu: Update packages to use 'non-copyleft' instead of 'bsd-style'.

* gnu/packages/avr.scm, gnu/packages/compression.scm,
  gnu/packages/curl.scm, gnu/packages/cyrus-sasl.scm,
  gnu/packages/databases.scm, gnu/packages/firmware.scm,
  gnu/packages/flex.scm, gnu/packages/fontutils.scm,
  gnu/packages/gd.scm, gnu/packages/ghostscript.scm,
  gnu/packages/gnunet.scm, gnu/packages/graphics.scm,
  gnu/packages/hugs.scm, gnu/packages/image.scm,
  gnu/packages/linux.scm, gnu/packages/mail.scm,
  gnu/packages/maths.scm, gnu/packages/mit-krb5.scm,
  gnu/packages/python.scm, gnu/packages/rdf.scm,
  gnu/packages/ssh.scm, gnu/packages/tcl.scm,
  gnu/packages/xdisorg.scm, gnu/packages/xiph.scm,
  gnu/packages/yasm.scm, gnu/packages/zip.scm: Use 'non-copyleft'
  instead of 'bsd-style'.