ti: unify Kconfig with other vendors

Rename WL_TI to WLAN_VENDOR_TI to match with other vendor configs and make sure
that it's enabled by default in new configs. Convert menuconfigs to regular
configs to unify the wireless drivers menuconfig. Part of reorganising wireless
drivers directory and Kconfig.

Also remove WLCORE dependency to WL_TI. It should not be needed as WLCORE is
already under if  WLAN_VENDOR_TI.

Signed-off-by: Kalle Valo <kvalo@codeaurora.org>