rtc-cmos driver and support

Here's the latest version of an "rtc-cmos" driver, which lets PCs (and other systems now using drivers/char/rtc.c) use the same RTC class framework that other Linuxes use.

- Patch #1 is the rtc-cmos driver itself. Configure PNPACPI and up it comes ... in vanilla mode.

- Patch #2 adds platform_device support for x86 PCs, so you can get that same vanilla functionality without PNPACPI.

- Patch #3 adds the first non-vanilla functionality, exporting some extensions (notably, longer alarms) that ACPI knows about.

This is all pretty clean, and AFAICT ready to merge. On hardware I have handy, it's a clean replacement for drivers/char/rtc.c code.

This particular version doesn't supplant the /proc/acpi/alarm mechanism, since I ripped that logic out for now. Eventually that can (and should!!) vanish(*), in favor of the portable userspace interfaces supported by earlier patch versions, but I figure there's no rush for that just now.

- Dave

(*) I'd be interested in hearing from anyone who actually uses
that interface ... if there is anyone. What do you do with it, and how.