selftests: ublk: kublk: simplify feat_map definition

selftests: ublk: kublk: simplify feat_map definition

Simplify the definition of feat_map by introducing a helper macro
FEAT_NAME to avoid having to type the feature name twice. As a side
effect, this changes the names in the feature list to be the full macro
name instead of the abbreviated names that were used before, but this is
a good change for clarity.

Using the full feature macro names ruins the alignment of the output, so
change the output format to put each feature's hex value before its
name, as this is easier to align nicely. The output now looks as
follows:

root# ./kublk features
ublk_drv features: 0x7fff
0x1               : UBLK_F_SUPPORT_ZERO_COPY
0x2               : UBLK_F_URING_CMD_COMP_IN_TASK
0x4               : UBLK_F_NEED_GET_DATA
0x8               : UBLK_F_USER_RECOVERY
0x10              : UBLK_F_USER_RECOVERY_REISSUE
0x20              : UBLK_F_UNPRIVILEGED_DEV
0x40              : UBLK_F_CMD_IOCTL_ENCODE
0x80              : UBLK_F_USER_COPY
0x100             : UBLK_F_ZONED
0x200             : UBLK_F_USER_RECOVERY_FAIL_IO
0x400             : UBLK_F_UPDATE_SIZE
0x800             : UBLK_F_AUTO_BUF_REG
0x1000            : UBLK_F_QUIESCE
0x2000            : UBLK_F_PER_IO_DAEMON
0x4000            : unknown

Signed-off-by: Uday Shankar <ushankar@purestorage.com>
Reviewed-by: Ming Lei <ming.lei@redhat.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>