wifi: move raycs, wl3501 and rndis_wlan to legacy directory

To clean up drivers/net/wireless move the old drivers drivers left in the
directory to a new "legacy" directory. I did consider adding
CONFIG_WLAN_VENDOR_LEGACY like other vendors have but then dropped the idea as
these are really old drivers and hopefully we get to remove them soon.

There should be no changes in compilation or in Kconfig options, merely moving files.

Signed-off-by: Kalle Valo <kvalo@kernel.org>
Link: https://lore.kernel.org/r/20230227121732.8967-3-kvalo@kernel.org