phy: samsung: add support for exynos7870 USB PHY

phy: samsung: add support for exynos7870 USB PHY

The USB PHY used by the Exynos7870 SoC has a single USB 2.0 interface.
Add its dedicated variant enum, compatible, and init/exit functions.

The PHY enable bit of Exynos7870's PHY is different in contrast to that
of Exynos850 and most Exynos PHYs. To allow this change, a simple if
condition is added in exynos_usbdrd_phy_isol() which changes the
bitmask. Since the variant enum is required, the function argument is
changed to accept the driver data itself.

Reviewed-by: Mattijs Korpershoek <mkorpershoek@kernel.org>
Signed-off-by: Kaustabh Chakraborty <kauschluss@disroot.org>
Signed-off-by: Minkyu Kang <mk7.kang@samsung.com>