phy: microchip: PHY_SPARX5_SERDES should depend on ARCH_SPARX5

The Microchip Sparx5 SerDes PHY is present only Microchip Sparx5 SoCs.
Hence add a dependency on ARCH_SPARX5, to prevent asking the user about
this driver when configuring a kernel without support for Sparx5 SoCs.

Fixes: 2ff8a1ee

 ("phy: Add Sparx5 ethernet serdes PHY driver")
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Link: https://lore.kernel.org/r/20210331081937.367408-1-geert+renesas@glider.be
Signed-off-by: Vinod Koul <vkoul@kernel.org>