set a default one in mkhelper.cfg

Signed-off-by: Leah Rowe <leah@libreboot.org>

this is bloat, because it's something the user can already
do at runtime configuration anyway.

set it to a reasonable default of 8 seconds instead of 5,
and don't honour the timeout variable in target.cfg.

this will be documented in the next release.

Signed-off-by: Leah Rowe <leah@libreboot.org>

Command: ./vendor download kcma-d8-rdimm_16mb

Output was:

include/lib.sh: line 115: kcma-d8-rdimm=config/vendor: No such file or directory

That will have to be audited later on, but the recent
more stringent error checking in vendor.sh triggered
this previously untriggered error message. The error
was in fact already occuring before, silently.

Anyway, mitigate by renaming all coreboot targets so
that they do not contain hyphens in the name. This
should avoid triggering errors in that eval command,
on line 115 in lib.sh

Signed-off-by: Leah Rowe <leah@libreboot.org>