wilc1000: move wilc driver out of staging

WILC1000 is an IEEE 802.11 b/g/n IoT link controller module. The
WILC1000 connects to Microchip AVR/SMART MCUs, SMART MPUs, and other
processors with minimal resource requirements with a simple
SPI/SDIO-to-Wi-Fi interface.

WILC1000 driver has been part of staging for few years. With
contributions from the community, it has improved significantly. Full
driver review has helped in achieving the current state.
The details for those reviews are captured in 1 & 2.

[1]. https://lore.kernel.org/linux-wireless/1537957525-11467-1-git-send-email-ajay.kathat@microchip.com/
[2]. https://lore.kernel.org/linux-wireless/1562896697-8002-1-git-send-email-ajay.kathat@microchip.com/

Signed-off-by: Ajay Singh <ajay.kathat@microchip.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>