x86/boot/compressed: Only build mem_encrypt.S if AMD_MEM_ENCRYPT=y

Avoid building the mem_encrypt.o object if memory encryption support is
not enabled to begin with.

Signed-off-by: Ard Biesheuvel <[e-mail]>
Signed-off-by: Borislav Petkov <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]

arch/x86/boot/compressed/Makefile

···
 ifdef CONFIG_X86_64
 	vmlinux-objs-y += $(obj)/ident_map_64.o
 	vmlinux-objs-y += $(obj)/idt_64.o $(obj)/idt_handlers_64.o
-	vmlinux-objs-y += $(obj)/mem_encrypt.o
+	vmlinux-objs-$(CONFIG_AMD_MEM_ENCRYPT) += $(obj)/mem_encrypt.o
 	vmlinux-objs-y += $(obj)/pgtable_64.o
 	vmlinux-objs-$(CONFIG_AMD_MEM_ENCRYPT) += $(obj)/sev.o
 endif

arch/x86/boot/compressed/mem_encrypt.S

···
 
 	.data
 
-#ifdef CONFIG_AMD_MEM_ENCRYPT
 	.balign	8
 SYM_DATA(sme_me_mask,		.quad 0)
 SYM_DATA(sev_status,		.quad 0)
···
 	.word	. - boot32_idt - 1
 	.long	0
 SYM_DATA_END(boot32_idt_desc)
-#endif