dt-bindings: ata: apm,xgene-ahci: Add apm,xgene-ahci-v2 support

The "apm,xgene-ahci-v2" compatible has been in use for a long time, but
was undocumented. It doesn't require clocks or phys.

Remove the "apm,xgene-ahci-pcie" compatible which isn't used anywhere
while we're here.

Signed-off-by: Rob Herring (Arm) <robh@kernel.org>
Signed-off-by: Damien Le Moal <dlemoal@kernel.org>