cpu/x86/acpi: Add assignments to ACPI_Sn enums

Explicitly assign numerical values to the enumerated sleep state
values.

BUG=b:153854742

Signed-off-by: Marshall Dawson <marshalldawson3rd@gmail.com>
Change-Id: I1de2e7f65a2dc3f8a9a1c5fd83d164871a4a2b96
Reviewed-on: https://review.coreboot.org/c/coreboot/+/40338
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Raul Rangel <rrangel@chromium.org>
Reviewed-by: Angel Pons <th3fanbus@gmail.com>

src/arch/x86/include/arch/acpi.h

@@ -979,13 +979,14 @@ void acpi_resume(void *wake_vec);
 void mainboard_suspend_resume(void);
 void *acpi_find_wakeup_vector(void);
 
+/* ACPI_Sn assignments are defined to always equal the sleep state numbers */
 enum {
-	ACPI_S0,
-	ACPI_S1,
-	ACPI_S2,
-	ACPI_S3,
-	ACPI_S4,
-	ACPI_S5,
+	ACPI_S0 = 0,
+	ACPI_S1 = 1,
+	ACPI_S2 = 2,
+	ACPI_S3 = 3,
+	ACPI_S4 = 4,
+	ACPI_S5 = 5,
 };
 
 #if CONFIG(ACPI_INTEL_HARDWARE_SLEEP_VALUES) \