Changes

card_key_provider: use case-insensitive field names

It is common in CSV files that the columns have uppercase names, so we
have adopted this scheme when we started using the card_key_provider.

This also means that the API of the card_key_provider_get() and
card_key_provider_get_field() function now implicitly requires
uppercase field names like 'ICCID', 'ADM1', etc.

Unfortunately this may be unreliable, so let's convert the field
names to uppercase as soon as we receive them. This makes the API
case-insensitive and gives us the assurance that all field names
we ever work with are in uppercase.

Related: SYS#7725
Change-Id: I9d80752587e2ccff0963c10abd5a2f42f5868d79