ARM: bcm2835_defconfig: Explicitly restore CONFIG_DEBUG_FS

The commit 0e4a459f ("tracing: Remove unnecessary DEBUG_FS dependency")
accidentally dropped the DEBUG FS support in bcm2835_defconfig. So
restore the config as before the commit.

Reported-by: Marek Szyprowski <m.szyprowski@samsung.com>
Fixes: 0e4a459f ("tracing: Remove unnecessary DEBUG_FS dependency")
Signed-off-by: Stefan Wahren <stefan.wahren@i2se.com>
Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>