sm501: fixup allocation code to be 64bit resource compliant

As pointed out by Andrew Morton, we have a problem when setting the 64bit
resources option.  Alter the allocation routines to remove the need to use
the start and end fields, use the proper HEAD_PANEL/HEAD_CRT and update
the comments.

Note, we also fix the bug where we failed to check the size of the
CRT memory allocation.

[akpm@linux-foundation.org: cleanup]
Signed-off-by: Ben Dooks <ben-linux@fluff.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>