Devices which use of-platdata have their own platdata. However, in many
cases the driver will have its own auto-alloced platdata, for use with the
device tree. The ofdata_to_platdata() method converts the device tree
settings to platdata.

With of-platdata we would not normally allocate the platdata since it is
provided by the U_BOOT_DEVICE() declaration. However this is inconvenient
since the of-platdata struct is closely tied to the device tree properties.
It is unlikely to exactly match the platdata needed by the driver.

In fact a useful approach is to declare platdata in the driver like this:

struct r3288_mmc_platdata {
	struct dtd_rockchip_rk3288_dw_mshc of_platdata;
	/* the 'normal' fields go here */
};

In this case we have dt_platadata available, but the normal fields are not
present, since ofdata_to_platdata() is never called. In fact driver model
doesn't allocate any space for the 'normal' fields, since it sees that there
is already platform data attached to the device.

To make this easier, adjust driver model to allocate the full size of the
struct (i.e. platdata_auto_alloc_size from the driver) and copy in the
of-platdata. This means that when the driver's bind() method is called,
the of-platdata will be present, followed by zero bytes for the empty
'normal field' portion.

A new DM_FLAG_OF_PLATDATA flag is available that indicates that the platdata
came from of-platdata. When the allocation/copy happens, the
DM_FLAG_ALLOC_PDATA flag will be set as well. The dtoc tool is updated to
output the platdata_size field, since U-Boot has no other way of knowing
the size of the of-platdata struct.

Signed-off-by: Simon Glass <sjg@chromium.org>