tf-a-next: cope with new RF-A tree layout

Since RF-A commit "chore(rust): move all RF-A files to the top
directory", the rust/ directory does not exist anymore. Update the
`build_package.sh` and static checks scripts to cope with that.

Signed-off-by: Sandrine Afsa <sandrine.afsa@arm.com>
Change-Id: I2bafffa5742119a6439a8902c0d486fcd30d8f18
5 files changed