Remove TARGET_CPU_SMP.

There are no more users of TARGET_CPU_SMP in the current codebase.
Expert users should set "-smp" in DEX2OAT_TARGET_INSTRUCTION_SET_FEATURES
for targets that run on a single-core CPU.

Change-Id: Ib94865f05a92c9a4622540cebc18ded4bdfa6363
Signed-off-by: Serban Constantinescu <serban.constantinescu@arm.com>