defconfig: fsm9900: Disable the DEVMEM kernel config

/dev/mem is no longer needed on the target. Remove the support of
memory device driver.

Change-Id: I95cef6bc7df4b6cf0d432c0fdd7a9c68b21a819a
Acked-by: Jie Luo <jluo@qti.qualcomm.com>
Signed-off-by: Venkatesh Yadav Abbarapu <quicvenkat@codeaurora.org>