ACPI: Handle CONFIG_ACPI=n better from linux/acpi.h

linux/acpi.h is the top level header for interfacing
with the ACPI sub-system, so acpi_disabled should be
up there instead of down in asm/acpi.h -- particularly
since asm/acpi.h doesn't exist for all architectures.

Same story for acpi_table_parse(), which is a top-level
API to Linux/ACPI.

This is necessary for building some code that
used to always depend on CONFIG_ACPI=y, but will soon
also need to build with CONFIG_ACPI=n.

Signed-off-by: Feng Tang <feng.tang@intel.com>
Signed-off-by: Len Brown <len.brown@intel.com>