zram: Drop allarch

* runtime dependencies are TUNE_PKGARCH causing do_package_write_*
  task to have different signature for MACHINEs with different
  TUNE_PKGARCH
* move kernel-module-zram to RRECOMMENDS, because signature handler
  is excluding kernel-module-* dependencies only from RRECOMMENDS and
  also because some machine can have zram enabled in kernel and
  kernel-module-zram won't exist.

Signed-off-by: Martin Jansa <Martin.Jansa@gmail.com>