CPU table removal comment

[Till Straumann]

I noticed that with the CPU table gone
exinit now always calls bsp_xxx_hook().

While the BSP certainly can override these hooks
by defining it's own versions there is currently
no way to call the generic version from libbsp/shared
from the BSP's 'special' hook -- something that I'd consider
desirable.

IMO, an additional level of indirection is required
(was previously provided by the CPU table).
E.g., the bsp_xxx_hook()s could be simple
wrappers  calling bsp_xxx_hook_generic().
If a BSP provides it's own bsp_xxx_hook it still
could call bsp_xxx_hook_generic() from there...

-- T.