efi: Add GRUB_PE32_MAGIC definition

Add a generic GRUB_PE32_MAGIC definition for the PE 'MZ' tag and delete
the existing one in arm64/linux.h.

Update arm64 Linux loader to use this new definition.

Signed-off-by: Leif Lindholm <leif.lindholm@linaro.org>

include/grub/arm64/linux.h

@@ -23,8 +23,6 @@
 
 #define GRUB_ARM64_LINUX_MAGIC 0x644d5241 /* 'ARM\x64' */
 
-#define GRUB_EFI_PE_MAGIC	0x5A4D
-
 /* From linux/Documentation/arm64/booting.txt */
 struct grub_arm64_linux_kernel_header
 {

include/grub/efi/pe32.h

@@ -45,6 +45,8 @@
 
 #define GRUB_PE32_MSDOS_STUB_SIZE	0x80
 
+#define GRUB_PE32_MAGIC			0x5a4d
+
 /* According to the spec, the minimal alignment is 512 bytes...
    But some examples (such as EFI drivers in the Intel
    Sample Implementation) use 32 bytes (0x20) instead, and it seems