ARM: dts: exynos: Add port map to Exynos5250 AHCI node

Exynos AHCI (SATA) controller has only one port for SATA device. According
to AHCI driver bindings (ata/ahci-platform.txt), if the bootloader doesn't
program the PORTS_IMPL register to proper value, the available port map has
to be provided by 'ports-implemented' device tree property. This fixes
SATA operation on Exynos5250-based boards since Linux v4.5.

Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>
Signed-off-by: Krzysztof Kozlowski <krzk@kernel.org>