Add DEXPREOPT_BOOTCLASSPATH_DEX_FILES to DEXPREOPT_GEN_DEPS

Anything that might be used by dexpreopt.sh needs to be listed
in DEXPREOPT_GEN_DEPS to make sure it is up to date if
dexpreopt.sh has never run before and generated its .d file.

Bug: 124062553
Test: lunch aosp_blueline-userdebug
      m out/target/product/blueline/obj/APPS/Gallery2_intermediates/dexpreopt.zip
      lunch aosp_sailfish-userdebug
      m out/target/product/sailfish/obj/APPS/Gallery2_intermediates/dexpreopt.zip
Change-Id: I2608f68d1a2157f9c95bd136eb82010aceed1c59