rtlwifi: rtl8821ae: Add VHT rate descriptors

Device RTL8821AE is the first if the rtlwifi devices to implement 802.11ac
capability. As a result, VHT rate descriptors are needed. In addition, the
driver is converted to use the descriptors in rtlwifi.

Signed-off-by: Larry Finger <Larry.Finger@lwfinger.net>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>