acpi: Comply with ACPI specification by making _STR unicode strings

_STR should return Unicode string. From ACPI spec:
6.1.10 _STR (String)
The _STR object evaluates to an Unicode string that describes the
device or thermal zone.

BUG=NA
TEST=Check the changed _STR in SSDT to see if Unicode() macro is used

Signed-off-by: Cliff Huang <cliff.huang@intel.com>
Change-Id: I1f4b55a268c1dadbae456afe5821ae161b8e15a5
Reviewed-on: https://review.coreboot.org/c/coreboot/+/77695
Reviewed-by: Eric Lai <eric_lai@quanta.corp-partner.google.com>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Jérémy Compostella <jeremy.compostella@intel.com>

src/acpi/acpigen_dptf.c

@@ -488,7 +488,7 @@ void dptf_write_STR(const char *str)
 	if (!str)
 		return;
 
-	acpigen_write_name_string("_STR", str);
+	acpigen_write_name_unicode("_STR", str);
 }
 
 void dptf_write_fan_options(bool fine_grained, int step_size, bool low_speed_notify)