MAINTAINERS: Add Marek and Shimoda-san as R-Car PCIE co-maintainers

At the end of the v5.3 upstream development cycle I stepped down
from my role at Renesas.

Pass maintainership of the R-Car PCIE to Marek and Shimoda-san.

Signed-off-by: Simon Horman <horms@verge.net.au>
Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Acked-by: Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>
Acked-by: Marek Vasut <marek.vasut+renesas@gmail.com>