[MTD] [MAPS] add support for Nvidia MCP55 to ck804xrom

This patch extends the existing MAPS driver for the Nvidia CK804 chipset
(ck804xrom.c) to also work on the Nvidia MCP55 chipset. As both chipsets
are rather similar, suporting them both with the same driver is easy.

Signed-off-by: Carl-Daniel Hailfinger <c-d.hailfinger.devel.2006@gmx.net>
Signed-off-by: David Woodhouse <dwmw2@infradead.org>