tc2: rename CPU internal codenames to the external ones

Hunter ELP, Hunter, Hayes change to Cortex X4, Cortex A720, Cortex A520
respectively.

Rename all occurrences of the three to their new replacements with what
is essentially a search and replace.

Resulting patches were tested with:
./build-scp.sh clean && ./build-scp.sh build && ./build-tfa.sh build && ./build-flash-image.sh deploy
starting from a clean build and applying the new patches. Then booting
to a buildroot shell.

While we're at it, specify that Booker is in fact CoreLink CI-700.

Signed-off-by: Boyan Karatotev <boyan.karatotev@arm.com>