feat(imx8mq): remove empty bl31_plat_runtime_setup

Having this empty definition is actively harmful, as it prevents the
default weak function to be used, which does a switch of the console
state.

Signed-off-by: Lucas Stach <l.stach@pengutronix.de>
Change-Id: I3b78e0c524c4907714036dba573a44d8f9c48b09

plat/imx/imx8m/imx8mq/imx8mq_bl31_setup.c

@@ -227,11 +227,6 @@ unsigned int plat_get_syscnt_freq2(void)
 	return COUNTER_FREQUENCY;
 }
 
-void bl31_plat_runtime_setup(void)
-{
-	return;
-}
-
 #ifdef SPD_trusty
 void plat_trusty_set_boot_args(aapcs64_params_t *args)
 {