Add phony target to check all PCF ELF prebuilts

Add phony target check-elf-prebuilt-product-copy-files that asserts
PRODUCT_COPY_FILES doesn't have ELF prebuilts.
This helps triage PCF ELF errors by providing a convenient target to
check / list all errors.

Bug: 140560012
Bug: 156534160
Test: lunch aosp_cf_x86_phone
Test: m USE_NDK_TRANSLATION_BINARY=true \
  check-elf-prebuilt-product-copy-files -k
Change-Id: Ic7fa43c10b0c30b3b1d9b7c2fae75cc6ea4a3513