Move dexpreopt image selection out of dexpreopt_gen

Instead of passing both the module and global dexpreopt image
selection into dexpreopt_gen, determine the correct dexpreopt
image in Make.  This allows the Make dexpreopt rule to only
depend on the necessary boot images, preventing an order-only
dependency on the 32-bit boot image for a 64-bit only module.

Also stop using the boot image "location" as an input, only
track the real path, which will be converted to the "location"
that dex2oat expects when constructing the command line in
dexpreopt_gen.

Removes support for the unused LOCAL_DEX_PREOPT_IMAGE_LOCATION
variable.

Test: m checkbuild
Change-Id: I2e3e1d30fdfed92fb08e6cc1c9515edf8d99c7f0