move simplebusvar.h so it can be used without ifdef
ok kettenis@ phessler@

constify struct cfattach

remove uneeded includes in md armv7 files

based on include-what-you-use suggestions

Add omcm(4), omclock(4) and omsysc(4) drivers that support the new bus
structure that is used in current mainline Linux device trees.

ok jsg@