MAINTAINERS: Add myself as the I3C subsystem maintainer

Create an entry for the I3C subsystem and mark it as maintained by me.
There's no official git repository, patchwork instance, mailing list or
website yet, but this will be added after the subsystem has been
accepted.

Signed-off-by: Boris Brezillon <boris.brezillon@bootlin.com>
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Changes in v10:
- None

Changes in v9:
- None

Changes in v8:
- None

Changes in v7:
- Add a ML (not created yet) and a git repo

Changes in v5:
- Add the sysfs ABI file
1 file changed