x86, acpi, tboot: Have a ACPI os prepare sleep instead of calling tboot_sleep.

The ACPI suspend path makes a call to tboot_sleep right before
it writes the PM1A, PM1B values. We replace the direct call to
tboot via an registration callback similar to __acpi_register_gsi.

CC: Len Brown <len.brown@intel.com>
Acked-by: Joseph Cihula <joseph.cihula@intel.com>
Acked-by: Rafael J. Wysocki <rjw@sisk.pl>
[v1: Added __attribute__ ((unused))]
[v2: Introduced a wrapper instead of changing tboot_sleep return values]
[v3: Added return value AE_CTRL_SKIP for acpi_os_sleep_prepare]
Signed-off-by: Tang Liang <liang.tang@oracle.com>
[v1: Fix compile issues on IA64 and PPC64]
[v2: Fix where __acpi_os_prepare_sleep==NULL and did not go in sleep properly]
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>

include/linux/acpi.h

@@ -359,4 +359,14 @@ static inline int suspend_nvs_register(unsigned long a, unsigned long b)
 }
 #endif
 
+#ifdef CONFIG_ACPI
+void acpi_os_set_prepare_sleep(int (*func)(u8 sleep_state,
+			       u32 pm1a_ctrl,  u32 pm1b_ctrl));
+
+acpi_status acpi_os_prepare_sleep(u8 sleep_state,
+				  u32 pm1a_control, u32 pm1b_control);
+#else
+#define acpi_os_set_prepare_sleep(func, pm1a_ctrl, pm1b_ctrl) do { } while (0)
+#endif
+
 #endif	/*_LINUX_ACPI_H*/