kernel: Invert polarity of memory pool's quad-block memory status field

Alters the use of the field so that a 1 bit indicates that the
associated block is available (i.e. can be allocated from the pool),
and a 0 bit indicates the block is unavailable (i.e. it is already
allocated or does not exist).

The revised definition of this field is more intuitive, since it follows
the conventional "1 = thing is present, 0 = this is not present" model.

Change-Id: Id133d1940aca0dd1c3c1672f989d0c0bb083ebc5
Signed-off-by: Allan Stephens <allan.stephens@windriver.com>