x86/Kconfig: Switch to ext4 in defconfigs

The current x86 and x86-64 defconfigs do not enable ext4, which
most current distributions default to.  Switch the defconfigs to
ext4, so they will boot on current systems without additional
configuration.

Signed-off-by: Josh Triplett <josh@joshtriplett.org>
Cc: Randy Dunlap <rdunlap@xenotime.net>
Cc: Suresh Siddha <suresh.b.siddha@intel.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/bd8a359506b7e1287c680823de16d67608ec52fe.1346649518.git.josh@joshtriplett.org


Signed-off-by: Ingo Molnar <mingo@kernel.org>