[POWERPC] Change rheap functions to use ulongs instead of pointers

The rheap allocation functions return a pointer, but the actual value is based
on how the heap was initialized, and so it can be anything, e.g. an offset
into a buffer.  A ulong is a better representation of the value returned by
the allocation functions.

This patch changes all of the relevant rheap functions to use a unsigned long
integers instead of a pointer.  In case of an error, the value returned is
a negative error code that has been cast to an unsigned long.  The caller can
use the IS_ERR_VALUE() macro to check for this.

All code which calls the rheap functions is updated accordingly.  Macros
IS_MURAM_ERR() and IS_DPERR(), have been deleted in favor of IS_ERR_VALUE().

Also added error checking to rh_attach_region().

Signed-off-by: Timur Tabi <timur@freescale.com>
Signed-off-by: Kumar Gala <galak@kernel.crashing.org>