arm64: efi: add efi-entry.o to targets instead of extra-$(CONFIG_EFI)

efi-entry.o is built on demand for efi-entry.stub.o, so you do not have
to repeat $(CONFIG_EFI) here. Adding it to 'targets' is enough.
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
Acked-by: Ard Biesheuvel <ardb@kernel.org>
Reviewed-by: Vincenzo Frascino <vincenzo.frascino@arm.com>

arch/arm64/kernel/Makefile

@@ -21,7 +21,7 @@ obj-y			:= debug-monitors.o entry.o irq.o fpsimd.o		\
 			   smp.o smp_spin_table.o topology.o smccc-call.o	\
 			   syscall.o
 
-extra-$(CONFIG_EFI)			:= efi-entry.o
+targets			+= efi-entry.o
 
 OBJCOPYFLAGS := --prefix-symbols=__efistub_
 $(obj)/%.stub.o: $(obj)/%.o FORCE