soc/intel/apollolake: allow DEBUG_SMI to work

The UART support is needed in SMM in order for DEBUG_SMI to
function.

BUG=chrome-os-partner:54262
TEST=Ran on reef with DEBUG_SMI enabled. Can observed SMI messages.

Change-Id: Ibd6b12e27d5776046b400adf72f24133b9e54af8
Signed-off-by: Aaron Durbin <adurbin@chromium.org>
Reviewed-on: https://review.coreboot.org/15151
Tested-by: build bot (Jenkins)
Reviewed-by: Furquan Shaikh <furquan@google.com>

src/soc/intel/apollolake/Makefile.inc

@@ -35,6 +35,7 @@ smm-y += pmutil.c
 smm-y += smihandler.c
 smm-y += spi.c
 smm-y += tsc_freq.c
+smm-y += uart_early.c
 
 ramstage-$(CONFIG_HAVE_ACPI_TABLES) += acpi.c
 ramstage-y += cpu.c