wifi: rt2x00: move helper functions up in file

Move register access helper functions up to the head of the file so
they can be used in all functions.

Signed-off-by: Daniel Golle <daniel@makrotopia.org>
Acked-by: Stanislaw Gruszka <stf_xl@wp.pl>
Signed-off-by: Kalle Valo <kvalo@kernel.org>
Link: https://lore.kernel.org/r/c27baa8efd5c29e2bcb2432925d9cdc5c913a125.1663445157.git.daniel@makrotopia.org