arm: rmobile: Add basic RZ/G2L family support

The Renesas RZ/G2L family includes the following ARM SoCs:

* RZ/G2L  (r9a07g044l)
* RZ/G2LC (r9a07g044c)
* RZ/G2UL (r9a07g043u)
* RZ/V2L  (r9a07g054l)

Support for individual SoCs and evaluation boards will be added in
separate patches.

Signed-off-by: Paul Barker <paul.barker.ct@bp.renesas.com>
Reviewed-by: Biju Das <biju.das.jz@bp.renesas.com>
Reviewed-by: Lad Prabhakar <prabhakar.mahadev-lad.rj@bp.renesas.com>
Reviewed-by: Marek Vasut <marek.vasut+renesas@mailbox.org>