clocksource/drivers/renesas-ostm: Add RZ/G2L OSTM support

RZ/G2L SoC has Generic Timer Module(a.k.a OSTM) which needs to
deassert the reset line before accessing any registers.

This patch adds an entry point for RZ/G2L so that we can deassert
the reset line in probe callback.

Signed-off-by: Biju Das <biju.das.jz@bp.renesas.com>
Reviewed-by: Lad Prabhakar <prabhakar.mahadev-lad.rj@bp.renesas.com>
Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
Link: https://lore.kernel.org/r/20211112184413.4391-4-biju.das.jz@bp.renesas.com


Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>