MAINTAINERS: Add entries for Renesas RZ/G2L MTU3a counter driver

Add the MAINTAINERS entries for the Renesas RZ/G2L MTU3a counter
driver.

Signed-off-by: Biju Das <biju.das.jz@bp.renesas.com>
Signed-off-by: Lee Jones <lee@kernel.org>
Link: https://lore.kernel.org/r/20230330111632.169434-6-biju.das.jz@bp.renesas.com