defconfig: Turn off slub debug on by default

Due to scm call request, 1 page is allocated frequently.
With slub debug on enabled by default, we will get order 1 pages
increased from order 0.
To avoid the potential issue of alloc pages, turn off the config
by default.

CRs-Fixed: 2252427
Change-Id: I0cf5b530b122190b99eebf46d0ff890944871e17
Signed-off-by: Zhenhua Huang <zhenhuah@codeaurora.org>