ACPI / tables: add DSDT AmlCode new declaration name support

A new naming rule was added in ACPICA version 20180427 changing
the DSDT AML code name from "AmlCode" to "dsdt_aml_code".

That change was made by commit 83b2fa94 "ACPICA: iASL: Enhance
the -tc option (create AML hex file in C)".

Tested:
ACPICA release version 20180427+.
ARM64: QCOM QDF2400
GCC: 4.8.5 20150623

Signed-off-by: Wang Dongsheng <dongsheng.wang@hxt-semitech.com>
[ rjw: Changelog ]
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>