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>

arch/arm/lib/crt0_aarch64_efi.S

@@ -8,6 +8,8 @@
  * This file is taken and modified from the gnu-efi project.
  */
 
+#include <asm-generic/pe.h>
+
 	.section	.text.head
 
 	/*
@@ -62,7 +64,7 @@ extra_header_fields:
 	 */
 	.long	_start - ImageBase		/* SizeOfHeaders */
 	.long	0				/* CheckSum */
-	.short	EFI_SUBSYSTEM			/* Subsystem */
+	.short	IMAGE_SUBSYSTEM_EFI_APPLICATION /* Subsystem */
 	.short	0				/* DllCharacteristics */
 	.quad	0				/* SizeOfStackReserve */
 	.quad	0				/* SizeOfStackCommit */

arch/arm/lib/crt0_arm_efi.S

@@ -8,6 +8,8 @@
  * This file is taken and modified from the gnu-efi project.
  */
 
+#include <asm-generic/pe.h>
+
 	.section	.text.head
 
 	/*
@@ -64,7 +66,7 @@ extra_header_fields:
 	 */
 	.long	_start - image_base		/* SizeOfHeaders */
 	.long	0				/* CheckSum */
-	.short	EFI_SUBSYSTEM			/* Subsystem */
+	.short	IMAGE_SUBSYSTEM_EFI_APPLICATION	/* Subsystem */
 	.short	0				/* DllCharacteristics */
 	.long	0				/* SizeOfStackReserve */
 	.long	0				/* SizeOfStackCommit */