Fix loading the hwpmc module when ACPI is enabled

[andrew]

Summary

In 0a9a4d2cd6092 a check for OPT_ACPI was added to the hwpmc Makefile
to fix loading the module in a kernel where ACPI has been disabled.
This broke loading the module when ACPI was enabled in the build as
OPT_ACPI isn't a Makefile macro so was always disabled.

Move this check to the C files where the DEV_ACPI macro does exist.

Sponsored by: Arm Ltd

[gnn]

LGTM

[emaste]

sys/arm64/arm64/cmn600.c

1–2

We should update the SPDX tag while here