efi_loader: fix building crt0 on arm

Before the patch an undefined constant EFI_SUBSYSTEM was used in the
crt0 code. The current version of binutils does not swallow the error.

https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=888403

The necessary constant IMAGE_SUBSYSTEM_EFI_APPLICATION is already
defined in pe.h. So let's factor out asm-generic/pe.h for the
image subsystem constants and use it in our assembler code.

IMAGE_SUBSYSTEM_SAL_RUNTIME_DRIVER does not exist in the specification
let's use IMAGE_SUBSYSTEM_EFI_ROM instead.

The include pe.h is only used in code maintained by Alex so let him be the
maintainer here too.

Reported-by: Andre Przywara <andre.przywara@arm.com>
Signed-off-by: Heinrich Schuchardt <xypron.glpk@gmx.de>
Tested-by: Vagrant Cascadian <vagrant@debian.org>
Signed-off-by: Alexander Graf <agraf@suse.de>
diff --git a/include/pe.h b/include/pe.h
index 4ef3e92..c3a19ce 100644
--- a/include/pe.h
+++ b/include/pe.h
@@ -11,6 +11,8 @@
 #ifndef _PE_H
 #define _PE_H
 
+#include <asm-generic/pe.h>
+
 typedef struct _IMAGE_DOS_HEADER {
 	uint16_t e_magic;	/* 00: MZ Header signature */
 	uint16_t e_cblp;	/* 02: Bytes on last page of file */
@@ -62,12 +64,6 @@
 
 #define IMAGE_NUMBEROF_DIRECTORY_ENTRIES 16
 
-/* PE32+ Subsystem type for EFI images */
-#define IMAGE_SUBSYSTEM_EFI_APPLICATION         10
-#define IMAGE_SUBSYSTEM_EFI_BOOT_SERVICE_DRIVER 11
-#define IMAGE_SUBSYSTEM_EFI_RUNTIME_DRIVER      12
-#define IMAGE_SUBSYSTEM_SAL_RUNTIME_DRIVER      13
-
 typedef struct _IMAGE_OPTIONAL_HEADER64 {
 	uint16_t Magic; /* 0x20b */
 	uint8_t  MajorLinkerVersion;