efi/libstub: move efi_system_table global var into separate object

To avoid pulling in the wrong object when using the libstub static
library to build the decompressor, define efi_system_table in a separate
compilation unit.
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>

drivers/firmware/efi/libstub/Makefile

@@ -66,7 +66,8 @@ $(obj)/lib-%.o: $(srctree)/lib/%.c FORCE
 	$(call if_changed_rule,cc_o_c)
 
 lib-$(CONFIG_EFI_GENERIC_STUB)	+= efi-stub.o fdt.o string.o intrinsics.o \
-				   $(patsubst %.c,lib-%.o,$(efi-deps-y))
+				   $(patsubst %.c,lib-%.o,$(efi-deps-y)) \
+				   systable.o
 
 lib-$(CONFIG_ARM)		+= arm32-stub.o
 lib-$(CONFIG_ARM64)		+= arm64-stub.o

drivers/firmware/efi/libstub/efi-stub.c

@@ -57,8 +57,6 @@
 static u64 virtmap_base = EFI_RT_VIRTUAL_BASE;
 static bool flat_va_mapping = (EFI_RT_VIRTUAL_OFFSET != 0);
 
-const efi_system_table_t *efi_system_table;
-
 static struct screen_info *setup_graphics(void)
 {
 	efi_guid_t gop_proto = EFI_GRAPHICS_OUTPUT_PROTOCOL_GUID;

drivers/firmware/efi/libstub/systable.c

+// SPDX-License-Identifier: GPL-2.0
+
+#include <linux/efi.h>
+#include <asm/efi.h>
+
+#include "efistub.h"
+
+const efi_system_table_t *efi_system_table;