nvs_util: Add changes to nvs part gen util
nvs_host_test: Add test case for keygen and keyfile paratmeters
(cherry picked from commit 9db19878927233d8d15a3a7fd568bfcc380a41d3)
Ideally suited for generating a binary externally, containing key-value pairs specific
to device manufacturers. Utility allows creation of a binary, compatible
with NVS structure, which can be separately flashed onto a new
partition. This helps device manufacturers set different values for
different devices, e.g. serial numbers, but using a single firmaware
image.