defconfig : msm: Add squashfs support for SA515M

Squashfs is needed for ramdisk in flashless boot.
Hence enable CONFIG_SQUASHFS & CONFIG_SQUASHFS_XZ in
sa515m kernel defconfig.

Change-Id: I5206b8602e453ad0ac207e72fe2287213b4957a8
Signed-off-by: Akshaya Bhat <akshayab@codeaurora.org>