util: Add coreboot log to VGA replay converter script

Signed-off-by: Alexandru Gagniuc <mr.nuke.me@gmail.com>
util/cb2replay.sh: Make VGA ports configurable

The location of the VGA IO ports depends on how coreboot sets up the
PCI BARs. Allow those ports to be changed by placing them in variables
rather than hardcoding in sed strings

Signed-off-by: Alexandru Gagniuc <mr.nuke.me@gmail.com>