Add version 3.12.1 (released the 2021-02-18) of firmware for Silabs
WF200. This firmware is necessary for the wfx driver currently hosted in
the staging/ directory of the Linux kernel.

Here the last modifications (only modifications tagged [LMAC] have an
impact on Linux):

New Features/Improvements:
    [1725] - [UMAC] Wi-Fi power mode API with 'listen_interval = 0' is
                    taken into account

Bug fixes:
    [1710] - [UMAC] Increase WPA3 connection authentication timeout
    [1712] - [LMAC] Avoid beacon collision in concurrent mode
    [1726] - [LMAC] Fix 'incoherent status and result_flags' warning
    [1730] - [UMAC] Fix incorrect packet abort leading to assert