tests/ci: Use QEMU blockdev declaration for all platforms

This patch uses the QEMU manpage-recommended '-blockdev' option instead
of '-drive' to declare block devices. This also makes the mandatory
'-device' declarations constant across all platforms, which fixes the
missing QEMU_DEVICES tarfs device declarations on all Makefile.<arch>
files.

Signed-off-by: Siva Mahadevan <me@svmhdvn.name>
Reviewed by: imp, lwhsu
Sponsored by: The FreeBSD Foundation
Differential Revision: https://reviews.freebsd.org/D51479