BUG/MEDIUM: ssl: OCSP must work with BoringSSL

BUG/MEDIUM: ssl: OCSP must work with BoringSSL

It's a regression from b3201a3e "BUG/MINOR: disable dynamic OCSP load
with BoringSSL". The origin bug is link to 76b4a12 "BUG/MEDIUM: ssl:
memory leak of ocsp data at SSL_CTX_free()": ssl_sock_free_ocsp()
shoud be in #ifndef OPENSSL_IS_BORINGSSL.
To avoid long #ifdef for small code, the BoringSSL part for ocsp load
is isolated in a simple #ifdef.

This must be backported in 2.2 and 2.1

(cherry picked from commit a73a222a9863e5f6763786845c1ff9e7e1038c3c)
Signed-off-by: William Lallemand <wlallemand@haproxy.org>
(cherry picked from commit f495e5d6a597e2e1caa965e963ef16103da545db)
Signed-off-by: William Lallemand <wlallemand@haproxy.org>