z/OS: change to available CipherSpecs

Two more CipherSpecs are available on z/OS®.

[z/OS]The following CipherSpecs, previously available only on distributed platforms, are now also available on z/OS:
  • ECDHE_RSA_AES_128_GCM_SHA256
  • ECDHE_RSA_AES_256_GCM_SHA384

This change was made under APAR PI97499.

For more information on platform availability for CipherSpecs, see Enabling CipherSpecs.