phy: renesas: phy-rcar-gen2: use select for GENERIC_PHY

Change the last "depends on GENERIC_PHY" to use select, like the
other 170+ Kconfig users do. This can help prevent circular
dependency issues.

Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Cc: Vinod Koul <vkoul@kernel.org>
Cc: Kishon Vijay Abraham I <kishon@kernel.org>
Cc: linux-phy@lists.infradead.org
Link: https://lore.kernel.org/r/20231204234917.23509-1-rdunlap@infradead.org


Signed-off-by: Vinod Koul <vkoul@kernel.org>