linuxkpi: Introduce a properly typed jiffies

Now that we have a long-sized tick counter, we can migrate to using
properly typed timeout parameters in various bits of the LinuxKPI. This
fixes a subtle incompatibility that is otherwise difficult to paper over
and leads to bugs when ticks values are sign-extended.

• Introduce a "jiffies" symbol in subr_ticks.S, declared only in the LinuxKPI as an unsigned long.
• Remove all references to "ticks" from the LinuxKPI.
• Convert interfaces to match Linux's type signatures where it makes sense.

Reviewed by: manu
Tested by: bz
Differential Revision: https://reviews.freebsd.org/D48523