libssh2: fix build failure with option no-ecdsa

libssh2 fails at do_compile if
DEPRECATED_CRYPTO_FLAGS = "no-ecdsa" is set in recipe:

../src/.libs/libssh2.so: undefined reference to
`LIBSSH2_KEX_METHOD_EC_SHA_HASH_CREATE_VERIFY'

References:
https://github.com/libssh2/libssh2/issues/549

Upstream patches:
https://github.com/libssh2/libssh2/commit/1f76151c92e1b52e9c24ebf06adc77fbd6c062bc



Signed-off-by: Stefan Ghinea <stefan.ghinea@windriver.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>