phy: exynos7-usbdrd: Update dependency for ARCH_EXYNOS

This PHY controller is also present on Exynos7 platform
in arch-exynos family.
So PHY_EXYNOS5_USBDRD should now depend on ARCH_EXYNOS.

Signed-off-by: Vivek Gautam <gautam.vivek@samsung.com>
Signed-off-by: Kishon Vijay Abraham I <kishon@ti.com>