Fix for loading progress for mapped files.

- fix the error code clash inside isFullyLoaded,
- work around buggy INCFS_IOC_GET_BLOCK_COUNT ioctl,
- additional feature flag.

Bug: 194143197
Test: atest IncFsTest
Change-Id: I1e2617842854db6335599b19b9b297ec9f677cf1
(cherry picked from commit 6405bab34a375002a569379068ff6102a6ff1a02)
5 files changed