sb/intel/lynxpoint: Add SerialIO UART console support

Derived from Broadwell and adapted to follow what soc/intel does. Note
that SERIALIO_UART_CONSOLE is meant to be selected from the mainboards
which expose a SerialIO UART. UART_FOR_CONSOLE also needs to be set in
mainboard Kconfig accordingly.

It is possible that some of the UART configuration steps in bootblock
are unnecessary. However, some of the steps turn off power management
features and others are undocumented: omitting them could cause weird
issues.

Finally, add a config file to ensure the code gets build-tested.

Tested on out-of-tree Compal LA-A992P, SerialIO UART 0 can be used to
receive coreboot and SeaBIOS logs.

Change-Id: Ifb3460dd50ed03421a38f03c80f91ae9fd604022
Signed-off-by: Angel Pons <th3fanbus@gmail.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/52489
Reviewed-by: Nico Huber <nico.h@gmx.de>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
diff --git a/configs/config.google_panther.pch_serialio_uart b/configs/config.google_panther.pch_serialio_uart
new file mode 100644
index 0000000..5f7f4c7
--- /dev/null
+++ b/configs/config.google_panther.pch_serialio_uart
@@ -0,0 +1,5 @@
+# Configuration used to build-test Lynx Point SerialIO UART console code.
+CONFIG_VENDOR_GOOGLE=y
+CONFIG_BOARD_GOOGLE_PANTHER=y
+CONFIG_SERIALIO_UART_CONSOLE=y
+# CONFIG_DRIVERS_UART_8250IO is not set