target-alpha: Register VMStateDescription for AlphaCPU

target-alpha: Register VMStateDescription for AlphaCPU

Commit b758aca1f6cdb175634812b79f5560c36c902d00 (target-alpha: Enable
the alpha-softmmu target.) introduced cpu_{save,load}() functions but
didn't define CPU_SAVE_VERSION, so they were never registered.

Drop cpu_{save,load}() and register the VMStateDescription via DeviceClass.
This operates on the AlphaCPU object instead of CPUAlphaState.

Reviewed-by: Juan Quintela <quintela@redhat.com>
Acked-by: Richard Henderson <rth@twiddle.net>
Signed-off-by: Andreas Färber <afaerber@suse.de>