libacpi: fixes for iasl >= 20180427

libacpi: fixes for iasl >= 20180427

New versions of iasl have introduced improved C file generation, as
reported in the changelog:

iASL: Enhanced the -tc option (which creates an AML hex file in C,
suitable for import into a firmware project):
  1) Create a unique name for the table, to simplify use of multiple
SSDTs.
  2) Add a protection #ifdef in the file, similar to a .h header file.

The net effect of that on generated files is:

-unsigned char AmlCode[] =
+#ifndef __SSDT_S4_HEX__
+#define __SSDT_S4_HEX__
+
+unsigned char ssdt_s4_aml_code[] =

The above example is from ssdt_s4.asl.

Fix the build with newer versions of iasl by stripping the '_aml_code'
suffix from the variable name on generated files.

Signed-off-by: Roger Pau Monné <roger.pau@citrix.com>
Reviewed-by: Wei Liu <wei.liu2@citrix.com>
Acked-by: Andrew Cooper <andrew.cooper3@citrix.com>
Release-acked-by: Juergen Gross <jgross@suse.com>