acpi: Add an __ACPI__ preprocessor symbol

The ASL compiler cannot handle C structures and the like so needs some
sort of header guard around these.

We already have an __ASSEMBLY__ #define but it seems best to create a new
one for ACPI since the rules may be different.

Add the check to a few files that ACPI always includes.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>
Reviewed-by: Wolfgang Wallner <wolfgang.wallner@br-automation.com>

include/acpi/acpi_table.h

@@ -21,6 +21,8 @@
 #define ACPI_RSDP_REV_ACPI_1_0	0
 #define ACPI_RSDP_REV_ACPI_2_0	2
 
+#if !defined(__ACPI__)
+
 /*
  * RSDP (Root System Description Pointer)
  * Note: ACPI 1.0 didn't have length, xsdt_address, and ext_checksum
@@ -389,6 +391,8 @@ struct __packed acpi_spcr {
 	u32 reserved2;
 };
 
+#endif /* !__ACPI__*/
+
 #include <asm/acpi_table.h>
 
 #endif /* __ACPI_TABLE_H__ */