acpi: remove some acpi-specific compiler definitions in favor of standard ones.

- Check if __linux__ is defined in include/acpi/platform/acenv.h, instead
  of -D_LINUX (defined by drivers/acpi/Makefile).
- Remove -D_LINUX from custom CFLAGS.
- Remove include path of include/acpi, since all headers are looked for in
  include/acpi.

drivers/acpi/Makefile

@@ -4,7 +4,7 @@
 
 export ACPI_CFLAGS
 
-ACPI_CFLAGS	:= -D_LINUX -Os -Iinclude/acpi
+ACPI_CFLAGS	:= -Os
 
 ifdef CONFIG_ACPI_DEBUG
   ACPI_CFLAGS	+= -DACPI_DEBUG_OUTPUT

include/acpi/platform/acenv.h

@@ -97,8 +97,8 @@
 
 /*! [Begin] no source code translation */
 
-#if defined(_LINUX)
-#include "aclinux.h"
+#if defined(__linux__)
+#include <acpi/platform/aclinux.h>
 
 #elif defined(_AED_EFI)
 #include "acefi.h"