lib: rsa: use actual OpenSSL 1.1.0 EVP MD API

Since OpenSSL 1.1.0, EVP_MD_CTX_create() is EVP_MD_CTX_new()
                     EVP_MD_CTX_destroy() is EVP_MD_CTX_free()
                     EVP_MD_CTX_init() is EVP_MD_CTX_reset()

As there's no need to reset a newly created EVP_MD_CTX, moreover
EVP_DigestSignInit() does the reset, thus call to EVP_MD_CTX_init()
can be dropped.
As there's no need to reset an EVP_MD_CTX before it's destroyed,
as it will be reset by EVP_MD_CTX_free(), call to EVP_MD_CTX_reset()
is not needed and can be dropped.

Signed-off-by: Yann Droneaud <ydroneaud@opteya.com>