Clarify unsigned int type in AIDL program id

Clarified that the value in ProgramIdentifier in AIDL broadcast radio
HAL should be unsigned 64-bit int, but is represented as signed int
since unsigned int types are not supported in AIDL.

Bug: 299489486
Test: m -j
(cherry picked from https://googleplex-android-review.googlesource.com/q/commit:40a58baa2cf0380dcab908a6f1e3cf8fd11d351c)
Merged-In: I2f35cefebdf1b5e39bf48cab896b077c4cb6c2e4
Change-Id: I2f35cefebdf1b5e39bf48cab896b077c4cb6c2e4