ARM: shmobile: bockw: define FPGA address and rename iomem variable

Bock-W board will needs more board specific ioremap() method.
This patch tidyup current FPGA specific settings

Signed-off-by: Kuninori Morimoto <kuninori.morimoto.gx@renesas.com>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>