usb: exynos: describe driver in KConfig

Describe better which driver applies to which SoC, to make configuring
kernel for Samsung SoC easier.

Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@canonical.com>
Link: https://lore.kernel.org/r/20210924133005.111564-1-krzysztof.kozlowski@canonical.com


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>