android: skip building drivers as modules

Few Android drivers e.g. uid_cputime and PPPoLAC/oPNS,
keyreset/combo, cpufreq_interactive etc.. fail to build
as kernel modules. Instead of fixing the build lets
make these drivers non-modular (switch config to "bool"
from "tristate" in Kconfig) since Android doesn't
support building kernel modules anyway.

Signed-off-by: Amit Pundir <amit.pundir@linaro.org>