defconfig : msm : Enable squashfs xattr support for SA515M

Squashfs Extended attribute support is needed for SELinux
which will be used in flashless boot.Hence enable
CONFIG_SQUASHFS_XATTR in sa515m defconfig.

Change-Id: I901c234d66df1868b0ce825c3e1e9cad3cb50751
Signed-off-by: Pavankumar Vijapur <pvijapur@codeaurora.org>