mb/amd/mandolin: select ACPI driver for internal memory mapped UARTs

In order for Linux to find and use the SoC's integrated UARTs, they need
to be exposed in ACPI.

BUG=b:165020060
TEST=Linux detects the SoC's integrated UARTs.

Change-Id: Iaa66657b88f62b2067c865c3e1945b7bdbf9be23
Signed-off-by: Felix Held <felix-coreboot@felixheld.de>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/44529
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Raul Rangel <rrangel@chromium.org>
Reviewed-by: Angel Pons <th3fanbus@gmail.com>

src/mainboard/amd/mandolin/Kconfig

@@ -10,6 +10,7 @@ config BOARD_SPECIFIC_OPTIONS
 	select BOARD_ROMSIZE_KB_8192 if BOARD_AMD_MANDOLIN
 	select AZALIA_PLUGIN_SUPPORT
 	select HAVE_ACPI_RESUME
+	select DRIVERS_UART_ACPI
 	select PICASSO_CONSOLE_UART if !AMD_LPC_DEBUG_CARD
 
 config FMDFILE