ARM: renesas: Factor out DRAM setup on R-Car Gen3

Pull DRAM layout configuration code into rcar-common.c instead of
having it in multiple copies across board files. This poses no
change for Salvator-X/XS, ULCB and Ebisu boards, however it adds
a bit of extra code for Draak and Eagle boards, which now gain
the capability of being passed in the DRAM layout by the ATF.

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