engines/libzbc: Enable trim for libzbc I/O engine

engines/libzbc: Enable trim for libzbc I/O engine

The trim workload to zoned block devices is supported as zone reset, and
this feature is available for I/O engines which support both zoned
devices and trim workload. Libzbc I/O engine supports zoned devices but
lacks trim workload support. To enable trim support with libzbc I/O
engine, remove the check which inhibited trim from requests to libzbc
I/O engine. Also set file open flags for trim same as write, and call
zbd_do_io_u_trim() for trim I/O.

Of note is that libzbc I/O engine now can support trim to sequential
write required zones only. The trim I/Os to conventional zones are
reported as an error.

Signed-off-by: Shin'ichiro Kawasaki <shinichiro.kawasaki@wdc.com>
Reviewed-by: Dmitry Fomichev <dmitry.fomichev@wdc.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>