refactor: relocate Gerrit metadata LAVA job YAML generation

This change moves the Gerrit metadata LAVA job YAML generation logic
from `gen_fvp_yaml_template` into `gen_fvp_yaml`. There's no real
reason to run this step separately anymore, and having two templating
phases makes it awkward to template the file (because second-phase
templating expressions need to be escaped).

Change-Id: Ib404b4fd275e0feb52a76699c5f060f651931527
Signed-off-by: Chris Kay <chris.kay@arm.com>
1 file changed