kbuild: scripts/kconfig/Makefile cleanup and fixes

This patch set:
Changes the update-po-config target to work when make is run from KBUILD_OUTDIR.
Changes the update-po-config target to reflectg the new layout of arch/um.
Adds a check to only build kxgettext when needed.
Changes the qconf and gconf targets to change hostprogs-y when they are being built like nconf and mconf instead of defining *-objs. Cleans up the clean-files definitions.
Silences comands unless V=1

Please discard my previous patch: "kbuild: scripts/kconfig/Makefile cleanup and fixes"

Thanks,

Peter