acpi: Add a pseudo-bus for APEI devices to manage resources

[jhb]

Summary

Different APEI tables can reuse the same registers (and sometimes
different views of the same register, e.g. 32- vs 64-bit mappings of
the same register). To enable this sharing, apei0 now acts as a bus
device managing a pool of allocated resources and handing out mappings
to child devices which handle individual tables.

Most of the previous apei(4) driver has been moved into a new
hest0 device that is a child of apei0.

Sponsored by: Netflix

[jhb]

Fix a malloc type mismatch noted by Claude

[imp]

sys/dev/acpica/acpi_apei_bus.c

114

Why create a fake one?