x86/boot: Don't add the EFI stub to targets, again

This is a re-commit of

  da05b14 ("x86/boot: Don't add the EFI stub to targets")

after the tagged patch incorrectly reverted it.

vmlinux-objs-y is added to targets, with an assumption that they are all
relative to $(obj); adding a $(objtree)/drivers/...  path causes the
build to incorrectly create a useless
arch/x86/boot/compressed/drivers/...  directory tree.

Fix this just by using a different make variable for the EFI stub.

Fixes: cb8bda8 ("x86/boot/compressed: Rename efi_thunk_64.S to efi-mixed.S")
Signed-off-by: Ben Segall <bsegall@google.com>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Reviewed-by: Ard Biesheuvel <ardb@kernel.org>
Cc: stable@vger.kernel.org # v6.1+
Link: https://lore.kernel.org/r/xm267ceukksz.fsf@bsegall.svl.corp.google.com

Author: Benjamin Segall

arch/x86/boot/compressed/Makefile

@@ -105,9 +105,9 @@ vmlinux-objs-$(CONFIG_UNACCEPTED_MEMORY) += $(obj)/mem.o
 
 vmlinux-objs-$(CONFIG_EFI) += $(obj)/efi.o
 vmlinux-objs-$(CONFIG_EFI_MIXED) += $(obj)/efi_mixed.o
-vmlinux-objs-$(CONFIG_EFI_STUB) += $(objtree)/drivers/firmware/efi/libstub/lib.a
+vmlinux-libs-$(CONFIG_EFI_STUB) += $(objtree)/drivers/firmware/efi/libstub/lib.a
 
-$(obj)/vmlinux: $(vmlinux-objs-y) FORCE
+$(obj)/vmlinux: $(vmlinux-objs-y) $(vmlinux-libs-y) FORCE
 	$(call if_changed,ld)
 
 OBJCOPYFLAGS_vmlinux.bin :=  -R .comment -S