ACPI: tables: Add __nonstring annotations for unterminated strings

ACPI: tables: Add __nonstring annotations for unterminated strings

When a character array without a terminating NUL character has a static
initializer, GCC 15's -Wunterminated-string-initialization will only
warn if the array lacks the "nonstring" attribute[1]. Mark the 4-byte
ACPI identifier arrays with __nonstring (and the new __nonstring_array)
to correctly identify the char arrays as "not C strings" and thereby
eliminate the many warnings like this:

In file included from include/acpi/actbl.h:371,
                 from include/acpi/acpi.h:26,
                 from include/linux/acpi.h:26,
                 from drivers/acpi/tables.c:19:
include/acpi/actbl1.h:30:33: warning: initializer-string for array of 'char' truncates NUL terminator but destination lacks 'nonstring' attribute (5 chars into 4 available) [-Wunterminated-string-initialization]
   30 | #define ACPI_SIG_BERT           "BERT"  /* Boot Error Record Table */
      |                                 ^~~~~~
drivers/acpi/tables.c:400:9: note: in expansion of macro 'ACPI_SIG_BERT'
  400 |         ACPI_SIG_BERT, ACPI_SIG_BGRT, ACPI_SIG_CPEP, ACPI_SIG_ECDT,
      |         ^~~~~~~~~~~~~

Link: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=117178
Signed-off-by: Kees Cook <kees@kernel.org>
Link: https://patch.msgid.link/20250415232028.work.843-kees@kernel.org
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>