init: allow loading of external ramdisk.

-Instead of loading the built in ramdisk, if there is one at
the static location below, load it instead.
s2w: refactor reset and isolate.

-Isolate s2w functions in preparation for dt2w.
Initial Import DoubleTap2Wake
d2w: register keys
dt2w: cytma340 - plugin the touchscreen
d2tw: add to defconfig