watchdog: fix several MODULE_PARM_DESC strings

Fix MODULE_PARM_DESC() strings in several watchdog drivers.
Some are simple as add a parenthesis.
Others are problems from __stringify() being used on a
variable name instead of a macro name, so the variable name
is produced in the string instead of its build-time value.
In these cases, create a macro for the value so that the
module param description string is useful.

Only pc87413_wdt has been built (due to toolchains).

Signed-off-by: Randy Dunlap <randy.dunlap@oracle.com>
Signed-off-by: Wim Van Sebroeck <wim@iguana.be>