kernel: am335x pmic power-off

XXX: Code doesn't run, gets a pagefault on first reg write 0x44e3e06c
Maybe the clock for the RTC module isn't enabled?

XXX: Code is a bit out of control. I originally thought I'd just have
to write to a couple of registers. There were some additional setup steps
that I didn't foresee and the amount of code has grown a lot. It needs
to be re-factored. Perhaps I could have an RTC driver that sets
everything up, freezes the clock, and then the kernel unfreezes the
clock (1 register write) to allow the reset to happen.