Add support for creating QBSP package

QBSP is a Qt specific Board Support Package that can be installed with
the Qt SDK or MaintenanceTool and contains a system image and a toolchain.
The toolchain is automatically registered to the QtCreator.

The recipes used for creating the system image and the toolchain can be
configured with QBSP_IMAGE_TASK and QBSP_SDK_TASK. The files wanted for
the system image can be further configured with QBSP_IMAGE_CONTENT,
with a list of files located in DEPLOY_DIR_IMAGE folder. By default,
.img and .conf files are used from the selected image recipe.

QBSP_INSTALLER_COMPONENT defines the location in the Qt installer tree
where the QBSP is shown and QBSP_VERSION defines the version for the
components. The QBSP is installed to path defined by QBSP_INSTALL_PATH.

The regular SDK creation can now reuse the same image package .7z, so
update upload script to use it instead of creating new package.

Task-number: QTBUG-57018
Change-Id: Id1e7cc4ab3998a7d450f23ed603b8e676b314d63
Reviewed-by: Iikka Eklund <iikka.eklund@qt.io>
Reviewed-by: Teemu Holappa <teemu.holappa@qt.io>