x86/sgx: Use ENCLS mnemonic in <kernel/cpu/sgx/encls.h>

Current minimum required version of binutils is 2.30, which supports ENCLS
instruction mnemonic.

Replace the byte-wise specification of ENCLS with this proper mnemonic.

No functional change intended.

Signed-off-by: Uros Bizjak <ubizjak@gmail.com>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Reviewed-by: Jarkko Sakkinen <jarkko@kernel.org>
Link: https://lore.kernel.org/20250616085716.158942-1-ubizjak@gmail.com