rdfremont*: rename all rdfremont manifest to rdv3

Neoverse Reference Design platform RD-Fremont has been renamed to RD-V3.
Similarly, the variant 1 and 2 has also been renamed. Update all
manifest names to reflect this change.

Change-Id: I771315f925852cc9891a758065e7cb81169612e5
Signed-off-by: Vijayenthiran Subramaniam <vijayenthiran.subramaniam@arm.com>