Consolidate bootcount code into drivers/bootcount

This patch moves all bootcount implementations into a common
directory: drivers/bootcount. The generic bootcount driver
is now usable not only by powerpc platforms, but others as well.

Signed-off-by: Stefan Roese <sr@denx.de>
Cc: Heiko Schocher <hs@denx.de>
Cc: Valentin Longchamp <valentin.longchamp@keymile.com>
Cc: Christian Riesch <christian.riesch@omicron.at>
Cc: Manfred Rudigier <manfred.rudigier@omicron.at>
Cc: Mike Frysinger <vapier@gentoo.org>
Cc: Rob Herring <rob.herring@calxeda.com>
Cc: Reinhard Meyer <reinhard.meyer@emk-elektronik.de>
Tested-by: Valentin Longchamp <valentin.longchamp@keymile.com>
Tested-by: Christian Riesch <christian.riesch@omicron.at>
Acked-by: Rob Herring <rob.herring@calxeda.com>
Acked-by: Mike Frysinger <vapier@gentoo.org>