ata: Make pata_of_platform.c compile again and work on non-PPC platforms

This patch adds missing #includes, makes the driver selectable on
non-PPC OF-enabled platforms and fixes property value accesses to
be correct in Little Endian system.

Cc: Anton Vorontsov <avorontsov@ru.mvista.com>
Signed-off-by: Pawel Moll <pawel.moll@arm.com>
Signed-off-by: Jeff Garzik <jgarzik@redhat.com>