se the number of possible localbus banks

Currently the fsl,*lbc devices support 8 banks (ie OR and BR registers).
This is adequate for most pq2 and pq3 processors, but not the MPC8280 which
has 12 banks.

Signed-Off-By: Mark Ware <mware@elphinstone.net>
Signed-off-by: Kumar Gala <galak@kernel.crashing.org>
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