sysutils/dmidecode: expand platform support

SMBIOS data is made available on all EFI platforms, including arm64,
arm, and riscv. Allow the port to be built for these architectures,
excluding the x86-specific utilities.

Reviewed by: lwhsu, emaste
Approved by: lwhsu (ports)
Sponsored by: The FreeBSD Foundation
Differential Revision: https://reviews.freebsd.org/D28244