[coreboot] Simplify buildrom's handling of coreboot-v2

This patch simplifies supporting v2 boards in buildrom. I like it pretty well, but I'm open to ways to simplify it even more. Mostly what I did was take the common operations out of the *.mk files and put them in coreboot.inc. I'll follow the patch with: svn rm packages/coreboot-v2/m57sli.mk svn rm packages/coreboot-v2/tyan-generic.mk svn rm packages/coreboot-v2/tyan-s2881.mk svn rm packages/coreboot-v2/tyan-s2891.mk svn rm packages/coreboot-v2/tyan-s2882.mk svn rm packages/coreboot-v2/asus_a8v-e_se.mk svn rm packages/coreboot-v2/qemu.mk svn rm packages/coreboot-v2/supermicro-h8dmr.mk They're no longer needed. Thanks, Myles Signed-off-by: Myles Watson <mylesgw@gmail.com>