Fix embedded build

1) Disable dexpreopt if DALVIK_VM_LIB isn't set up by the product.
2) DEX2OAT_TARGET_INSTRUCTION_SET_FEATURES is moved to config.mk,
for it's only decided by target arch.
3) Move Java module input from embedded.mk to base.mk.

Change-Id: Ife70b0cd8cee2e5c92f356c808affa56f494b49a