selftests/sgx: Provide per-op parameter structs for the test enclave

To add more operations to the test enclave, the protocol needs to allow
to have operations with varying parameters. Create a separate parameter
struct for each existing operation, with the shared parameters in struct
encl_op_header.

[reinette: rebased to apply on top of oversubscription test series]
Signed-off-by: Jarkko Sakkinen <jarkko@kernel.org>
Signed-off-by: Reinette Chatre <reinette.chatre@intel.com>
Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
Acked-by: Dave Hansen <dave.hansen@linux.intel.com>
Link: https://lkml.kernel.org/r/f9a4a8c436b538003b8ebddaa66083992053cef1.1636997631.git.reinette.chatre@intel.com