ARM: hikey: hi6220: Migrate over to DM_SERIAL and use UART3 by default.

Use DM for the pl01x serial driver on hikey. Also allow UART0 or
UART3 to be chosen via Kconfig.

By default we now output to UART3 as the latest version of ATF outputs
to this UART. Also UART3 comes out on the LS connector, as opposed to
UART0 which goes to a unpopulated header.

As part of this change we also enable CONFIG_BOARD_EARLY_INIT_F and
call the pinmux configuration code for the UART. Before we were
relying on ATF having already configured the pin configuration.

NB: Upstream Linux kernel doesn't yet support UART3, so serial console
will still be output on UART0 when booting a upstream kernel.

Signed-off-by: Peter Griffin <peter.griffin@linaro.org>
Reviewed-by: Simon Glass <sjg@chromium.org>
diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
index 5a8d4b2..0b07e08 100644
--- a/arch/arm/Kconfig
+++ b/arch/arm/Kconfig
@@ -604,6 +604,7 @@
 	select ARM64
 	select DM
 	select DM_GPIO
+	select DM_SERIAL
 	  help
 	  Support for HiKey 96boards platform. It features a HI6220
 	  SoC, with 8xA53 CPU, mali450 gpu, and 1GB RAM.
@@ -612,7 +613,6 @@
 	bool "Support ls1021aqds"
 	select CPU_V7
 	select SUPPORT_SPL
-
 config TARGET_LS1021ATWR
 	bool "Support ls1021atwr"
 	select CPU_V7