[POWERPC] fsl_elbc_nand: factor out localbus defines

This is needed to support other localbus peripherals, such as
NAND on FSL UPM.

Signed-off-by: David Woodhouse <dwmw2@infradead.org>
Signed-off-by: Anton Vorontsov <avorontsov@ru.mvista.com>
Signed-off-by: Kumar Gala <galak@kernel.crashing.org>