ICP: gcm: Allocate hash subkey table separately

While evaluating other assembler implementations it turns out that
the precomputed hash subkey tables vary in size, from 8*16 bytes
(avx2/avx512) up to 48*16 bytes (avx512-vaes), depending on the
implementation.

To be able to handle the size differences later, allocate
`gcm_Htable` dynamically rather then having a fixed size array, and
adapt consumers.

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Attila Fülöp <attila@fueloep.org>
Closes #11102

module/icp/algs/modes/modes.c

@@ -152,6 +152,14 @@ crypto_free_mode_ctx(void *ctx)
 			vmem_free(((gcm_ctx_t *)ctx)->gcm_pt_buf,
 			    ((gcm_ctx_t *)ctx)->gcm_pt_buf_len);
 
+#ifdef CAN_USE_GCM_ASM
+		if (((gcm_ctx_t *)ctx)->gcm_Htable != NULL) {
+			gcm_ctx_t *gcm_ctx = (gcm_ctx_t *)ctx;
+			bzero(gcm_ctx->gcm_Htable, gcm_ctx->gcm_htab_len);
+			kmem_free(gcm_ctx->gcm_Htable, gcm_ctx->gcm_htab_len);
+		}
+#endif
+
 		kmem_free(ctx, sizeof (gcm_ctx_t));
 	}
 }