phy: Kconfig: Re-organize Exynos USB 2.0 PHY configs

Since the USB 2.0 PHYs are required with EHCI/OHCI USB drivers and
USB gadget controller supported by the DWC2 gadget driver, make it
depend on them and default to ARCH_EXYNOS as they are meant for
Exynos platforms. Also, make the sub-drivers silent options enabling
them based on the SoC platforms that they are meant to work with. This
will make life easier for end users who do not have any way knowing the
dependencies.

Signed-off-by: Sachin Kamat <sachin.kamat@samsung.com>
Reviewed-by: Jingoo Han <jg1.han@samsung.com>
Tested-by: Vivek Gautam <gautam.vivek@samsung.com>
Signed-off-by: Kishon Vijay Abraham I <kishon@ti.com>