arm64: dts: exynos: Keep LDO12 always-on on Espresso

LDO12 on Exynos7 Espresso board supplies power to VDDQ_UFS20_RESET, in
case this regulator is OFF, UFS host controller can not send command to
UFS device. To keep this supply ON, set regulator-always-on property for
this LDO.

Signed-off-by: Alim Akhtar <alim.akhtar@samsung.com>
Signed-off-by: Krzysztof Kozlowski <krzk@kernel.org>