x86, boot: Don't compile aslr.c when !CONFIG_RANDOMIZE_BASE

All the code in aslr.c gets compiled out if !CONFIG_RANDOMIZE_BASE, but
aslr.o itself still gets compiled in.  Eliminate it from the compile
entirely in that case.

This does not change the generated code at all, in either case.

Signed-off-by: Josh Triplett <josh@joshtriplett.org>