fix(rdv3): add console name to checksum calculation on RD-V3

The name field of console_info structure was missed in
checksum calculation. This is corrected by adding a new
helper checksum_calc() which computes the checksum in a
field agnostic manner.

Change-Id: I98d35d53e1faccf1221e8eddb122558ae359a2d5
Signed-off-by: Jerry Wang <Jerry.Wang4@arm.com>