defconfig: 8974: Increase default Kmemleak log size to 4000 from 400

The intention of this change is to help with memory leak
debugging, without any need to change the config file

Change-Id: Idc0b8cd4e0cd2c095accfad85f05481bf2647a47
Signed-off-by: Monu Surana <msurana@codeaurora.org>