devres: introduce Devres (Managed Device Resource) framework

devres: introduce Devres (Managed Device Resource) framework

In U-Boot's driver model, memory is basically allocated and freed
in the core framework.  So, low level drivers generally only have
to specify the size of needed memory with .priv_auto_alloc_size,
.platdata_auto_alloc_size, etc.  Nevertheless, some drivers still
need to allocate/free memory on their own in case they cannot
statically know the necessary memory size.  So, I believe it is
reasonable enough to port Devres into U-boot.

Devres, which originates in Linux, manages device resources for each
device and automatically releases them on driver detach.  With devres,
device resources are guaranteed to be freed whether initialization
fails half-way or the device gets detached.

The basic idea is totally the same to that of Linux, but I tweaked
it a bit so that it fits in U-Boot's driver model.

In U-Boot, drivers are activated in two steps: binding and probing.
Binding puts a driver and a device together.  It is just data
manipulation on the system memory, so nothing has happened on the
hardware device at this moment.  When the device is really used, it
is probed.  Probing initializes the real hardware device to make it
really ready for use.

So, the resources acquired during the probing process must be freed
when the device is removed.  Likewise, what has been allocated in
binding should be released when the device is unbound.  The struct
devres has a member "probe" to remember when the resource was
allocated.

CONFIG_DEBUG_DEVRES is also supported for easier debugging.
If enabled, debug messages are printed each time a resource is
allocated/freed.

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Acked-by: Simon Glass <sjg@chromium.org>