arm64: defconfig: Disable firmware sysfs fallback

Part of the enablement of SDMA on the IMX platforms, '7f4e4afa
("arm64: defconfig: Enable SDMA on i.mx8mq/8mm")' also enabled
CONFIG_FW_LOADER_USER_HELPER_FALLBACK, to allow "firmware loaded by
udev".

Unfortunately having the fallback enabled does, due to the 60 second
timeout, essentially requiring userspace to provide a firmware loader.
But systemd dropped the support for this interface back in 2014 and
because arm64 is the only architecture that has this enabled, there
doesn't seem to be any standard solution available.

Examples of this problem can be found in e.g. the ath10k driver, which
with a standard distro can take about 10 minutes before wlan0 appears.

The alternative to this patch would be to change these drivers to use
firmware_request_direct(), to avoid the sysfs fallback. But that would
prevent other systems, such as Android, to rely on a userspace firmware
loader to pick the firmware from a non-standard place, with just a
custom defconfig.

This patch therefor attempts to align the arm64 defconfig will all other
architectures in the upstream kernel.

Cc: Robin Gong <yibin.gong@nxp.com>
Cc: Shawn Guo <shawnguo@kernel.org>
Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>
Acked-by: Shawn Guo <shawnguo@kernel.org>
Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Link: https://lore.kernel.org/r/20210930215300.60290-1-bjorn.andersson@linaro.org