kv_config: Remove hard fail on too few pages
kv_config: Remove hard fail on too few pages

STORE_SECTORS is a hard requirement. If there are fewer than 2 pages
then the kvstore will not work, because the garbage collection process
relies on having at least two sectors to work with.
STORE_PAGES is a heuristic. It is a reasonable default to use if the
application does not specify the amount of flash to use for TDBStore.
But if an application knows that a smaller number of pages will suffice
for its specific needs, then that is valid and should be permitted.

mbedmicro/mbed,kjbracey-arm/mbed,mbedmicro/mbed,kjbracey-arm/mbed,mbedmicro/mbed,mbedmicro/mbed,kjbracey-arm/mbed,kjbracey-arm/mbed,mbedmicro/mbed