sys: Enable NVMe drivers on all architectures

The NVMe drivers are portable and are already included statically in
GENERIC on other architectures such as aarch64 and riscv64.

Reviewed by: imp
Sponsored by: Chelsio Communications
Differential Revision: https://reviews.freebsd.org/D44690

(cherry picked from commit 16e846fa1ed3c97419b55b292f77b0f4209f0875)