kernel.bbclass: Dont package kxgettext.o

kxgettext.o is generated when building ppc kernels
so we end up with packaging errors like

> ERROR: QA Issue: Architecture did not match (20 to 62) on
> /work/virtex5-poky-linux/linux-xilinx-2.6.38-r00/packages-split/kernel-dev/usr/src/kernel/scripts/kconfig/kxgettext.o

Signed-off-by: Khem Raj <raj.khem@gmail.com>
Signed-off-by: Saul Wold <sgw@linux.intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
Signed-off-by: Martin Jansa <Martin.Jansa@gmail.com>
Signed-off-by: Koen Kooi <koen@dominion.thruhere.net>