tools: ynl-gen: lift type requirement for attribute subsets

In case an attribute is used in a subset, the type has to be currently
specified. As the attribute is already defined in the original set, this
is a redundant information in yaml file, moreover, may lead to
inconsistencies.

Example:
attribute-sets:
    ...
    name: pin
    enum-name: dpll_a_pin
    attributes:
      ...
      -
        name: parent-id
        type: u32
      ...
  -
    name: pin-parent-device
    subset-of: pin
    attributes:
      -
        name: parent-id
        type: u32             <<<<<<<<<<<<<<<<<<<<<<<<<<<<<<<

Remove the requirement from schema files to specify the "type" for
attribute subsets.

Signed-off-by: Jiri Pirko <jiri@nvidia.com>
Reviewed-by: Jakub Kicinski <kuba@kernel.org>
Link: https://lore.kernel.org/r/20231006114436.1725425-2-jiri@resnulli.us


Signed-off-by: Jakub Kicinski <kuba@kernel.org>