docs(auth): add missing AUTH_PARAM_NV_CTR value

Section "Describing the authentication method(s)" of the Authentication
Framework documentation shows the authentication parameters types
(auth_param_type_t enum type) but is missing the AUTH_PARAM_NV_CTR
value. Add it.

Signed-off-by: Sandrine Bailleux <sandrine.bailleux@arm.com>
Change-Id: I7c9022badfb039bfa9f999ecee40f18b49e6764c
1 file changed