Correct dexopt for uniprocessors.

The SMP flag was defaulting to "true" for dexopt, even on uniprocessors.
With this change the VM now has three choices: dexopt for SMP, dexopt
for uniprocessor, or dexopt for current system.  The last is used for
just-in-time dexopt (used by -eng and -userdebug builds on bootstrap DEX
files) and installd dexopt (used for apps on all builds).

The dexopt used by the build system during -user builds will either be
explicitly SMP or explicitly uniprocessor, since "current system" has
no meaning when you're cross-dexopting.

Also, unified the dexopt control flags into a single enum.

(cherry-pick from dalvik-dev)

Change-Id: Id1d9c548ca8567585a28ef9ee911cc2ac6b116dd