powerpc: remove "config MPC10X_OPENPIC"

The last users of Kconfig symbol MPC10X_OPENPIC were removed in v2.6.27.
Its Kconfig entry can be removed now.

Signed-off-by: Paul Bolle <pebolle@tiscali.nl>
Signed-off-by: Kumar Gala <galak@kernel.crashing.org>