Return the number of blocks of storage associated with the device or
instance. Where a "block" is a unit of storage consisting of the number
of bytes returned by the package's "block-size" method. If the size cannot
be determined, the #blocks method returns the maximum unsigned integer
(which, because of Open Firmware's assumption of two's complement arithmetic,
is equivalent to the signed number -1). If the number of blocks exceeds
the range of an unsigned number, return 0 to alert the caller to try
the #blocks64 command.

Signed-off-by: Eric Snowberg <eric.snowberg@oracle.com>
Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>