ACPI: do not select ACPI_DOCK from ATA_ACPI

In March 2008 commit 0ac4a3c2 ("ACPI: fix
ATA_ACPI build") made CONFIG_ACPI_DOCK be selected by CONFIG_ATA_ACPI because
of a build error when CONFIG_ATA_ACPI=y and CONFIG_ACPI_DOCK=m.

However, in September 2008 commit 898b054f
("dock: make dock driver not a module") removed the possibility of having
CONFIG_ACPI_DOCK=m and therefore there is no need for selecting it when
CONFIG_ATA_ACPI=y.

This makes the kernel ~5 Kb smaller for people who don't have a dock by
allowing them to not have ACPI_DOCK compiled-in because of ATA_ACPI=y.

Signed-off-by: Carlos R. Mafra <crmafra@aei.mpg.de>
Cc: Shaohua Li <shaohua.li@intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Len Brown <len.brown@intel.com>