[coreboot] [PATCH]Avoid northbridge/southbridge specific rules in generic i386 code

[Patrick Georgi]

Hi,

attached patch makes "bigbootblock" use the romstraps build
infrastructure created for "tinybootblock" (chipset_bootblock_inc and
chipset_bootblock_lds) instead of using chipset specific rules in the
generic i386 Makefile.

It also adds rules for the romstraps of
* southbridge/nvidia/ck804
* southbridge/sis/sis966
* northbridge/via/vx800
for the benefit of both image layouts.

Signed-off-by: Patrick Georgi