The LV parser is not compiled correctly by more recent versions of GHC
because of more strict checks.

lvCommand is a surely non-empty list, but the compiler still refuses it
asking for explicitly management of the empty list case.

Instead of managing that case (that would be meaningless), the lvCommand
is split into lvCommand and lvParams, that can be used independently.

Signed-off-by: Michele Tartara <mtartara@google.com>
Reviewed-by: Klaus Aehlig <aehlig@google.com>