rt2x00: rt2800lib: move rt2800_drv_data declaration into rt2800lib.h

The rt2800_drv_data structure contains driver specific
information. Move the declaration into the rt2800lib.h
header which is a more logical place for it. Also fix
the comment style to avoid checkpatch warning.

The patch contains no functional changes, it is in
preparation for the next patch.

Signed-off-by: Gabor Juhos <juhosg@openwrt.org>
Signed-off-by: Daniel Golle <daniel@makrotopia.org>
Signed-off-by: Stanislaw Gruszka <sgruszka@redhat.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>