sh: hwblk base implementation

This patch is the hwblk base implementation, containing
structures and shared functions dealing with hardware blocks.

A each processor model should provide a list of hwblks and
describe which module stop bit that is associated with each
hwblck and how the hwblks are grouped together into areas.

The shared code keeps track of the usage count for each
hwblk and the areas. Fallback implementations for processor
specific code are also kept as weak symbols.

The clock framework, the runtime pm code and cpuidle will
all tie into this hwblk implementation.

Signed-off-by: Magnus Damm <damm@igel.co.jp>
Signed-off-by: Paul Mundt <lethal@linux-sh.org>