qt5virtualkeyboard: fix legal-info with 5.6

qt5virtualkeyboard 2.0 (shipped with Qt 5.6) doesn't contain any
"main" license files with the GPLv3 license text.

Conditionally remove LICENSE.GPL3 from QT5VIRTUALKEYBOARD_LICENSE_FILES
when Qt major version is set to 5.6.

Fixes:

	>>> qt5virtualkeyboard 2.0 Collecting legal info
	sha256sum: /home/gportay/src/buildroot/output/build/qt5virtualkeyboard-2.0/LICENSE.GPL3: No such file or directory
	ERROR: LICENSE.GPL3 has wrong sha256 hash:
	ERROR: expected: 8ceb4b9ee5adedde47b31e975c1d90c73ad27b6b165a1dcd80c7c545eb65b903
	ERROR: got     :
	ERROR: Incomplete download, or man-in-the-middle (MITM) attack

Also, the lipi-toolkit has a different filename between both supported
Qt major version (5.6 and latest).

Conditionally set the license in QT5VIRTUALKEYBOARD_LICENSE_FILES for
lipi-toolkit according to the Qt major version used.

Fixes:
	>>> qt5virtualkeyboard 2.0 Collecting legal info
	ERROR: No hash found for src/virtualkeyboard/3rdparty/openwnn/NOTICE
	ERROR: No hash found for src/virtualkeyboard/3rdparty/pinyin/NOTICE
	ERROR: No hash found for src/virtualkeyboard/3rdparty/tcime/COPYING
	sha256sum: /home/gportay/src/buildroot/output/build/qt5virtualkeyboard-2.0/src/virtualkeyboard/3rdparty/lipi-toolkit/MIT_LICENSE.txt: No such file or directory
	ERROR: src/virtualkeyboard/3rdparty/lipi-toolkit/MIT_LICENSE.txt has wrong sha256 hash:
	ERROR: expected: 7a45a9769d19545480a241230e6ea520b5156fac00930dcd69b6886749743d10
	ERROR: got     :
	ERROR: Incomplete download, or man-in-the-middle (MITM) attack

Signed-off-by: Gaël PORTAY <gael.portay@savoirfairelinux.com>
[Thomas: add hash for lipi-toolkit license file, tweak commit log.]
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>