phy: ti: usb2: fix OMAP_CONTROL_PHY dependency

With randconfig build testing on arm64, we can run into a configuration
that has CONFIG_OMAP_CONTROL_PHY=m and CONFIG_OMAP_USB2=y, which in turn
causes a link failure:

drivers/phy/ti/phy-omap-usb2.o: In function `omap_usb_phy_power':
phy-omap-usb2.c:(.text+0x17c): undefined reference to `omap_control_phy_power'

I could not come up with a good way to correctly describe the relation
of the two symbols, but if we just select CONFIG_OMAP_CONTROL_PHY
during compile testing, we can no longer run into the broken configuration.

Fixes: 6777cee3 ("phy: ti: usb2: Add support for AM654 USB2 PHY")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Kishon Vijay Abraham I <kishon@ti.com>