dt-bindings: timer: renesas: ostm: Document Renesas RZ/V2L OSTM

Document the General Timer Module(a.k.a OSTM) found on the RZ/V2L SoC.
OSTM module is identical to one found RZ/G2L SoC. No driver changes are
required as generic compatible string "renesas,ostm" will be used as a
fallback.

Signed-off-by: Lad Prabhakar <prabhakar.mahadev-lad.rj@bp.renesas.com>
Reviewed-by: Biju Das <biju.das.jz@bp.renesas.com>
Acked-by: Krzysztof Kozlowski <krzysztof.kozlowski@canonical.com>
Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: Rob Herring <robh@kernel.org>
Link: https://lore.kernel.org/r/20220227224845.27348-1-prabhakar.mahadev-lad.rj@bp.renesas.com