clocksource/drivers/renesas-ostm: Unconditionally enable reprobe support

clocksource/drivers/renesas-ostm: Unconditionally enable reprobe support

Previously, the OSTM driver's platform probe path was only enabled for
selected SoCs (e.g., RZ/G2L and RZ/V2H) due to issues on RZ/Ax (ARM32)
SoCs, which encountered IRQ conflicts like:

    /soc/timer@e803b000: used for clock events
    genirq: Flags mismatch irq 16. 00215201 (timer@e803c000) vs. 00215201 (timer@e803c000)
    Failed to request irq 16 for /soc/timer@e803c000
    renesas_ostm e803c000.timer: probe with driver renesas_ostm failed with error -16

These issues have since been resolved by commit 37385c0772a4
("clocksource/drivers/renesas-ostm: Avoid reprobe after successful early
probe"), which prevents reprobe on successfully initialized early timers.

With this fix in place, there is no longer a need to restrict platform
probing based on SoC-specific configs. This change unconditionally enables
reprobe support for all SoCs, simplifying the logic and avoiding the need
to update the configuration for every new Renesas SoC with OSTM.

Additionally, the `ostm_of_table` is now marked with `__maybe_unused` to
fix a build warning when `CONFIG_OF` is disabled.

RZ/A1 and RZ/A2 remain unaffected with this change.

Signed-off-by: Lad Prabhakar <prabhakar.mahadev-lad.rj@bp.renesas.com>
Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
Tested-by: Geert Uytterhoeven <geert+renesas@glider.be>
Link: https://lore.kernel.org/r/20250515182207.329176-3-prabhakar.mahadev-lad.rj@bp.renesas.com
Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>