lib: utils: Add SiFive test device

This patch factor-out SiFive test device related stuff into
it's own source file from qemu/virt platform. In future, we
can find SiFive test device address from device tree as well.

Signed-off-by: Anup Patel <anup.patel@wdc.com>
Reviewed-by: Atish Patra <atish.patra@wdc.com>