ANDROID: Enable CONFIG_EXPERT on microdroid kernels

CONFIG_EXPERT is useful for being able to control advanced kernel
features. Enable it for microdroid kernels to allow the kernel to
be optimized better for size.

No functional change.

Bug: 432329937
Change-Id: I24efaf5d6cca241b784e1e9d20538c7a84f2d3be
Signed-off-by: Isaac J. Manjarres <isaacmanjarres@google.com>