brcmfmac: Limit memory allocs to <64K

Some systems have problems with allocating memory allocation larger
then 64K. Often on unload/load or suspend/resume a failure is
reported: Could not allocate wiphy device. This patch makes the
escan intermediate storage buf dynamically allocated, and smaller
than 64K.

Reviewed-by: Arend Van Spriel <arend@broadcom.com>
Reviewed-by: Franky (Zhenhui) Lin <frankyl@broadcom.com>
Reviewed-by: Pieter-Paul Giesberts <pieterpg@broadcom.com>
Signed-off-by: Hante Meuleman <meuleman@broadcom.com>
Signed-off-by: Arend van Spriel <arend@broadcom.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>