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

commit 61de13df upstream.

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

Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
Signed-off-by: Borislav Petkov <bp@suse.de>
Link: https://lore.kernel.org/r/20221122161017.2426828-17-ardb@kernel.org


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>