x86/sgx: Add short descriptions to ENCLS wrappers

The SGX ENCLS instruction uses EAX to specify an SGX function and
may require additional registers, depending on the SGX function.
ENCLS invokes the specified privileged SGX function for managing
and debugging enclaves. Macros are used to wrap the ENCLS
functionality and several wrappers are used to wrap the macros to
make the different SGX functions accessible in the code.

The wrappers of the supported SGX functions are cryptic. Add short
descriptions of each as a comment.

Suggested-by: Dave Hansen <dave.hansen@linux.intel.com>
Signed-off-by: Reinette Chatre <reinette.chatre@intel.com>
Signed-off-by: Dave Hansen <dave.hansen@linux.intel.com>
Reviewed-by: Jarkko Sakkinen <jarkko@kernel.org>
Link: https://lkml.kernel.org/r/5e78a1126711cbd692d5b8132e0683873398f69e.1652137848.git.reinette.chatre@intel.com