Add wrapper function xpt_kv_get which gets a value based on its key
(or rather sends a XPT_KV_GET CCB to the SIM associated with the path).
Add wrapper function xpt_kv_set which sets the value (or rather sends
a XPT_KV_SET CCB to the SIM associated with the path).
Define XPT_KV_GET which allows periphs to lookup key values associated
with the path by the SIM, if it exists.
Define XPT_KV_SET which allows setting values for a key associated
with the path by the SIM, if it exists and is allowed.
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