soc/intel/apollolake: Implement global reset handling

Global reset enable bit is not cleared on reset. Therefore, clear
the bit early. Lock down 0xcf9 so that payload/OS can't issue
global reset.

BUG=chrome-os-partner:54149
BRANCH=none
TEST=none

Change-Id: I3ddf6dd82429b725c818bcd96e163d2ca0acd308
Signed-off-by: Andrey Petrov <andrey.petrov@intel.com>
Reviewed-on: https://review.coreboot.org/15199
Reviewed-by: Aaron Durbin <adurbin@chromium.org>
Tested-by: build bot (Jenkins)

src/soc/intel/apollolake/bootblock/bootblock.c

@@ -25,6 +25,7 @@
 #include <soc/mmap_boot.h>
 #include <soc/northbridge.h>
 #include <soc/pci_devs.h>
+#include <soc/pm.h>
 #include <soc/uart.h>
 #include <spi-generic.h>
 #include <timestamp.h>
@@ -153,6 +154,9 @@ void bootblock_soc_early_init(void)
 {
 	enable_pmcbar();
 
+	/* Clear global reset promotion bit */
+	global_reset_enable(0);
+
 	/* Prepare UART for serial console. */
 	if (IS_ENABLED(CONFIG_SOC_UART_DEBUG))
 		soc_console_uart_init();