wifi: move mac80211_hwsim and virt_wifi to virtual directory

To clean up drivers/net/wireless move the virtual drivers to a new virtual
directory. I did consider adding CONFIG_WLAN_VENDOR_VIRTUAL like other vendors
have but then dropped the idea as we are not real drivers.

There should be no changes in compilation or in Kconfig options, merely moving
files. The order in menuconfig is slightly changed, the virtual drivers are now
last in the list.

Signed-off-by: Kalle Valo <kvalo@kernel.org>
Link: https://lore.kernel.org/r/20230227121732.8967-2-kvalo@kernel.org