python3-pyqt5: enable SVG support

Add a bbappend for python3-pyqt5 to enable its QtSvg module that
exposes Qt's SVG support.  This is required for
agl-demo-control-panel.

Bug-AGL: SPEC-4952

Change-Id: Ic8ae0816227306139b6e14cbe6974bcfeffcef7f
Signed-off-by: Scott Murray <scott.murray@konsulko.com>
Reviewed-on: https://gerrit.automotivelinux.org/gerrit/c/AGL/meta-agl-demo/+/29345
Reviewed-by: Jan-Simon Moeller <jsmoeller@linuxfoundation.org>
ci-image-boot-test: Jenkins Job builder account
Tested-by: Jenkins Job builder account
Reviewed-by: Lisandro Perez Meyer <lpmeyer@ics.com>
ci-image-build: Jenkins Job builder account