Parcel: hasFileDescriptors warning

Calling this API on system parcelables may lead to
app compat issues. Call this out, since the API
is public. Call it out on hasBinders for good
measure.

Bugs: michaelwr@ (came up on internal code review)
Test: N/A
Change-Id: I94ad82129aca70d18b7ce8f6081e90e3e529731d