classes: create-spdx: Move to version specific class

In expectation of SPDX 3.0 support, move the create-spdx.bbclass ->
create-spdx-2.2.bbclass. The create-spdx.bbclass class still exists and
can be used if a user doesn't care about which specific version of SPDX
they get.

Signed-off-by: Joshua Watt <JPEWhacker@gmail.com>
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>