ARM: bcm2835: enable procfs and sysfs in defconfig

For some reason, support for proc and sysfs is currently disabled in
the bcm2835_defconfig, even though those filesystems are quite
essential even for very basic Linux userspace. As most defconfig have
them enabled by default, enable them as well in bcm2835_defconfig.

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Signed-off-by: Stephen Warren <swarren@wwwdotorg.org>