wifi: rtw89: fw: refine download flow to support variant firmware suits

To support download more than one firmware, adjust flow to download
firmware by unit of firmware suit. Then, flow becomes

 1. initial setup - disable/enable_wcpu
 2. for all firmware suits
 2.1. download WiFi CPU, and check ready
 2.2. download BB MCU, and check ready
 3. check status code to make sure all ready

Signed-off-by: Ping-Ke Shih <pkshih@realtek.com>
Signed-off-by: Kalle Valo <kvalo@kernel.org>
Link: https://lore.kernel.org/r/20230901073956.54203-8-pkshih@realtek.com