Add preliminary support for using SQLite for eap_user database

Add preliminary support for using SQLite for eap_user database

CONFIG_SQLITE=y option can now be used to allow the eap_user_file text
file to be replaced with a SQLite database
(eap_user_file=sqlite:/path/to/sqlite.db). hostapd.eap_user_sqlite
shows an example of how the database tables can be created for this
purpose. This commit does not yet include full functionality of the
text file format, but at least basic EAP-TTLS/MSCHAPv2 style
authentication mechanisms with plaintext passwords can be used for
tests.

Signed-hostap: Jouni Malinen <j@w1.fi>