defconfig: sdm845: Disable DEBUG_OBJECTS_RCU_HEAD to save memory

DEBUG_OBJECTS_RCU_HEAD has significant memory usage. In
cases of stress testing, where RCU gets excessive usage,
these debug objects increases memory pressure and yields
false positive memory issues. Disable by default.

Change-Id: I0fcc10e08b4d223552ecde9a17bdd3aad8deeaec
Signed-off-by: Channagoud Kadabi <ckadabi@codeaurora.org>