vendor.intel: double-quote Tcl values rather than brace-quoting.

vendor.intel: double-quote Tcl values rather than brace-quoting.

For unknown reasons, Quartus treats {foo} and "foo" in completely
different ways, which is not true for normal Tcl code; specifically,
it preserves the braces if they are used. Because of this, since
commit 6cee2804, the vendor.intel package was completely broken.