qtbase: enable xkbcommon support

qtbase: enable xkbcommon support

Add xkbcommon to PACKAGECONFIG in our qtbase bbappend so that Qt
keyboard support will work in e.g. PyQt5.

Bug-AGL: SPEC-4952

Change-Id: I7ff9b58a6779e1b154a60184ee4a3c4f304c41ee
Signed-off-by: Scott Murray <scott.murray@konsulko.com>
Reviewed-on: https://gerrit.automotivelinux.org/gerrit/c/AGL/meta-agl-demo/+/29342
ci-image-build: Jenkins Job builder account
Reviewed-by: Jan-Simon Moeller <jsmoeller@linuxfoundation.org>
Tested-by: Jenkins Job builder account
ci-image-boot-test: Jenkins Job builder account