Add SPI mode diagnostics for all post-MCP55 (nForce 5) chipsets from Nvidia

Huge thanks to Michael Karcher for reverse engineering the MCP67 chipset
and writing a spec. Due to this, we were able to use the chinese wall
technique for 100% clean room reverse engineering.

This patch doesn't touch any of the new registers, it only reads them.
Assuming that read has no side effects, this patch is a no-op and safe.

We need "flashrom -V" output from all post-MCP55 (nForce 5) chipset
boards. Please indicate if your board uses SPI flash or LPC flash (if
you know it). Note: That output is only helpful if it is created with
patched flashrom and if is from the first run of flashrom after a cold
boot (reset or Ctrl-Alt-Del is not sufficient). There is a pattern based
on which we can probably detect which flash type is present on the
board.

Thanks to Alessandro Polverini for testing earlier iterations of this
patch.

Note: The MCP67 should work. I guessed that the other recent Nvidia
chipsets would work in a similar way, and created a simplified
do-nothing catchall chipset enable function which dumps some info and
instructs the user to send more info.

Corresponding to flashrom svn r902.

Signed-off-by: Carl-Daniel Hailfinger <c-d.hailfinger.devel.2006@gmx.net>
Acked-by: Michael Karcher <flashrom@mkarcher.dialup.fu-berlin.de>
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