powerpc/83xx: make mpc830x_rdb use mpc83xx_setup_pci

Traditionally mpc830x_rdb board file searched for mpc8308-pcie devices.
However both in-kernel dts from the beginning declared those pcie units
as compatible with mpc8314-pci, which is handled by mpc83xx_setup_pci().

Drop special handling for mpc8308 and use common function instead.

Signed-off-by: Dmitry Eremin-Solenikov <dbaryshkov@gmail.com>
Signed-off-by: Kumar Gala <galak@kernel.crashing.org>