ARM: renesas: Mallocate bootparams on Gen3

The bootparams do not have to be at fixed location, they can be
dynamically mallocated instead. Make it so to get rid of another
fixed assignment.

Signed-off-by: Marek Vasut <marek.vasut+renesas@gmail.com>
Cc: Biju Das <biju.das.jz@bp.renesas.com>
Cc: Lad Prabhakar <prabhakar.mahadev-lad.rj@bp.renesas.com>