framework-nfc: add aconfig_declarations block

Add missing aconfig_declarations block to the framework-nfc
java_sdk_library soong module. Without this, soong doesn't know which
flags to tell metalava to retain, and metalava will effectively revert
all API changes in framework-nfc, even if the @FlaggedApi flag is
enabled.

Bug: 328923659
Test: TreeHugger
Merged-In: Iafa82071b613f9fdd590b605ab0b07cd587ecd0f
Change-Id: Iafa82071b613f9fdd590b605ab0b07cd587ecd0f