ARM: configs: at91: Enable options required for systemd

Even smaller embedded systems are using systemd these days, as
are test automation systems like KernelCI, so it is useful to be
able to use systemd on these boards by default. Enable options
that are missing in the at91_dt_defconfig, cgroups which is
critical and autofs4 which is less critical but causes warnings
on boot when not available.

Signed-off-by: Mark Brown <broonie@kernel.org>
Signed-off-by: Nicolas Ferre <nicolas.ferre@microchip.com>
Link: https://lore.kernel.org/r/20220505171043.553079-1-broonie@kernel.org