sh: r2dplus: Switch to DM PCI driver

Add DT entry for the DM PCI driver, update board configs
and drop ad-hoc board init code for the PCI bus. Instead,
let the DM PCI driver initialize and operate the hardware.

Signed-off-by: Marek Vasut <marek.vasut+renesas@gmail.com>
Cc: Nobuhiro Iwamatsu <iwamatsu@nigauri.org>