arm: convert sysdev_class to a regular subsystem

After all sysdev classes are ported to regular driver core entities, the
sysdev implementation will be entirely removed from the kernel.

Cc: Kukjin Kim <kgene.kim@samsung.com>
Cc: Russell King <linux@arm.linux.org.uk>
Cc: Ben Dooks <ben-linux@fluff.org>
Cc: Vinod Koul <vinod.koul@intel.com>
Cc: Boojin Kim <boojin.kim@samsung.com>
Cc: Linus Walleij <linus.walleij@linaro.org>
Cc: Lucas De Marchi <lucas.demarchi@profusion.mobi>
Cc: Heiko Stuebner <heiko@sntech.de>
Signed-off-by: Kay Sievers <kay.sievers@vrfy.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>