[coreboot] [PATCH]Various walkcbfs fixes

[Patrick Georgi]

Hi,

there were still a couple of bugs in walkcbfs, but I got them now.

This patch:
- makes walkcbfs capable of loading files other than the first
- look more closely for files, which should make the code robust
  against defective CBFS images, as long as the bootblock works

With this, I managed to boot both fallback and normal with tinybootblock.

Signed-off-by: Patrick Georgi <[e-mail]