arm64: defconfig: explicitly SLIMBUS_MSM_NGD as m

SLIMBUS_MSM_NGD should be m not y for the current
device to be normally boot up and function.
Explicitly mark CONFIG_SLIMBUS as m as well for
normal function.

Change-Id: I09502c2300f9ee5fe06a82146b5832a13a576cff
Signed-off-by: Maria Yu <aiquny@codeaurora.org>