defconfig: msm8996: Disable EXT2 and EXT3 FS configs

This is required to fix the VTS test case failures which are failing
as the kernel supports EXT2/EXT3 but the tools mkfs.ext2/mkfs.ext3
doesn't exist anymore.

Change-Id: Iceb44b1fdb3127b8f249dd1b2697d84fae318619
Signed-off-by: Naitik Bharadiya <bharad@codeaurora.org>