isa_common: allow multiple device instances

In some devices, there may be multiple isa bridges available from different
sources. Therefore, we allow multiple lpc devices to be generated so that
pcie bus won't show "none" anymore.
For example, in my AMD based Framework Laptop, there are two such
bridges. One is acpi hinted, another is from pcie.

Reviewed by: imp
Approved by: lwhsu (mentor)
MFC after: 2 weeks
Differential Revision: https://reviews.freebsd.org/D52815