phy: starfive: StarFive PHYs should depend on ARCH_STARFIVE

The various StarFive PHYs are only present on StarFive SoCs.  Hence add
a dependency on ARCH_STARFIVE, to prevent asking the user about these
drivers when configuring a kernel without StarFive SoC support.

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Acked-by: Changhuang Liang <changhuang.liang@starfivetech.com>
Link: https://lore.kernel.org/r/12097f6107a18e2f7cfb80f47ac7b27808e062c4.1690300076.git.geert+renesas@glider.be
Signed-off-by: Vinod Koul <vkoul@kernel.org>