MAINTAINERS: add Rust PHY abstractions for ETHERNET PHY LIBRARY

Adds me as a maintainer and Trevor as a reviewer.

The files are placed at rust/kernel/ directory for now but the files
are likely to be moved to net/ directory once a new Rust build system
is implemented.

Signed-off-by: FUJITA Tomonori <fujita.tomonori@gmail.com>
Signed-off-by: Trevor Gross <tmgross@umich.edu>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>