PHY: Ingenic: fix unconditional build of phy-ingenic-usb

Currently drivers/phy/ingenic/Makefile adds phy-ingenic-usb to targets
not depending on actual Kconfig symbol CONFIG_PHY_INGENIC_USB, so this
driver always gets built[-in] on every system.
Add missing dependency.

Fixes: 31de313dfdcf ("PHY: Ingenic: Add USB PHY driver using generic PHY framework.")
Signed-off-by: Alexander Lobakin <alobakin@pm.me>
Link: https://lore.kernel.org/r/20201222131021.4751-1-alobakin@pm.me
Signed-off-by: Vinod Koul <vkoul@kernel.org>

PHY: Ingenic: Add USB PHY driver using generic PHY framework.

Used the generic PHY framework API to create the PHY, this driver
supoorts USB OTG PHY used in JZ4770 SoC, JZ4775 SoC, JZ4780 SoC,
X1000 SoC, X1830 SoC and X2000 SoC.

Co-developed-by: 漆鹏振 (Qi Pengzhen) <aric.pzqi@ingenic.com>
Signed-off-by: 漆鹏振 (Qi Pengzhen) <aric.pzqi@ingenic.com>
Signed-off-by: 周琰杰 (Zhou Yanjie) <zhouyanjie@wanyeetech.com>
Tested-by: 周正 (Zhou Zheng) <sernia.zhou@foxmail.com>
Tested-by: H. Nikolaus Schaller <hns@goldelico.com>
Reviewed-by: Paul Cercueil <paul@crapouillou.net>
Link: https://lore.kernel.org/r/20201116141906.11758-4-zhouyanjie@wanyeetech.com
Signed-off-by: Vinod Koul <vkoul@kernel.org>