arm64/efi/libstub: Make screen_info accessible to the UEFI stub

Unlike on 32-bit ARM, where we need to pass the stub's version of struct
screen_info to the kernel proper via a configuration table, on 64-bit ARM
it simply involves making the core kernel's copy of struct screen_info
visible to the stub by exposing an __efistub_ alias for it.

Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Signed-off-by: Matt Fleming <matt@codeblueprint.co.uk>
Acked-by: Will Deacon <will.deacon@arm.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: David Herrmann <dh.herrmann@gmail.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Peter Jones <pjones@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-efi@vger.kernel.org
Link: http://lkml.kernel.org/r/1461614832-17633-21-git-send-email-matt@codeblueprint.co.uk
Signed-off-by: Ingo Molnar <mingo@kernel.org>
diff --git a/arch/arm64/include/asm/efi.h b/arch/arm64/include/asm/efi.h
index af40baa..fa09886 100644
--- a/arch/arm64/include/asm/efi.h
+++ b/arch/arm64/include/asm/efi.h
@@ -56,6 +56,9 @@
 #define __efi_call_early(f, ...)	f(__VA_ARGS__)
 #define efi_is_64bit()			(true)
 
+#define alloc_screen_info(x...)		&screen_info
+#define free_screen_info(x...)
+
 #define EFI_ALLOC_ALIGN		SZ_64K
 
 /*