brcmfmac: Set SDIO workqueue as WQ_HIGHPRI

brcmfmac: Set SDIO workqueue as WQ_HIGHPRI

This puts tasks submitted to the SDIO workqueue at the head of the queue
and runs them immediately. This gets higher RX throughput with the SDIO
bus.

This was originally submitted as [1]. The original author Wright Feng
reports

> throughput result with 43455(11ac) on 1 core 1.6 Ghz platform is
>     Without WQ_HIGGPRI TX/RX: 293/301 (mbps)
>     With    WQ_HIGHPRI TX/RX: 293/321 (mbps)

I tested this with a 43364(11bgn) on a 1 core 800 MHz platform and got
    Without WQ_HIGHPRI TX/RX: 16/19 (Mbits/sec)
    With    WQ_HIGHPRI TX/RX: 24/20 (MBits/sec)

[1] https://lore.kernel.org/linux-wireless/1584604406-15452-4-git-send-email-wright.feng@cypress.com/

Signed-off-by: Sean Anderson <sean.anderson@seco.com>
Reviewed-by: Arend van Spriel <aspriel@gmail.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>
Link: https://lore.kernel.org/r/20210802170904.3116223-1-sean.anderson@seco.com