This is in line with other platforms such as i.MX, which allow
specifying a debug port. As we can't use port indices because
the UARTs aren't mapped consecutively, allow specifying a hex
base at configuration time.

A side effect of this patch is that sama5d4's HAVE_AT91_DBGU2
is now honored as well. Previously anything besides DBGU0
defaulted to DBGU1.

Fixes: 06a0773ee31 ("ARM: at91: add sama5d4 soc support #2")
Reviewed-by: Sam Ravnborg <sam@ravnborg.org>
Tested-by: Sam Ravnborg <sam@ravnborg.org>
[afa: moved base address defaults to common/Kconfig]
Signed-off-by: Ahmad Fatoum <afa@pengutronix.de>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>