ARM: exynos_defconfig: Enable DYNAMIC_DEBUG and get rid of old ext3

DYNAMIC_DEBUG is quite useful for debugging kernels and should not cause
noticeable performance regressions.  It makes the kernel bigger (around 4%)
but this difference should not impact typical developer and reference
usage of this defconfig.

Sizes:
zImage-old:       4641496 bytes
zImage-new:       4811384 bytes

   text	   data	    bss	    dec	    hex	filename
7031229	2570916	 327016	9929161	 9781c9	vmlinux-old
72059215	2800052	 327016	10332989 9dab3d	vmlinux-new

Additionally, remove the EXT3_FS symbol because it is entirely replaced
by EXT4_FS.

Signed-off-by: Krzysztof Kozlowski <krzk@kernel.org>
Reviewed-by: Javier Martinez Canillas <javier@osg.samsung.com>