ACPI: Remove duplicate definitions of PREFIX

We already have a macro for PREFIX of "ACPI: " in
drivers/acpi/internal.h, so remove the duplicate ones
in ACPI drivers when internal.h is included.

Signed-off-by: Hanjun Guo <hanjun.guo@linaro.org>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>