devmap: eliminate unused arguments

The optional 'table' pointer is a legacy part of the interface, which
has been replaced by devmap_register_table()/devmap_add_entry(). The few
in-tree callers have already adapted to this, so it can be removed.

The 'l1pt' argument is already entirely unused within the function.

Reviewed by: andrew, markj
Sponsored by: The FreeBSD Foundation
Differential Revision: https://reviews.freebsd.org/D45319