[coreboot] [PATCH]CAR and Tiny bootblock for via/vt8454c (and fixes that help other via c7 based systems)

[Patrick Georgi]

Hi,

attached patch does:
- move the XIP_ROM_* flags to src/cpu/x86/Kconfig exclusively
- set them to span the last 64k, instead of the last 128k
  by default
- fixes via CAR for tiny bootblock
- enabled tiny bootblock for via/vt8454c

Other C7 based boards should be simple to adapt, too. They will however
require some refactoring if ROM mappings must be configured.

Signed-off-by: Patrick Georgi