ACPICA: Emit all unresolved method externals in a text block

Put all of the unresolved external method declarations in a single block,
since they are important and may cause the resulting disassembled ASL file
to not compile.
This patch only affects ACPICA utilities and is necessary to avoid adding
source code divergences between Linux and ACPICA upstream.

Signed-off-by: Bob Moore <robert.moore@intel.com>
Signed-off-by: Lv Zheng <lv.zheng@intel.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>